bluuebunny/crossref_metadata_2025 huggingface dataset:
PARAMETER IDENTIFICATION TECHNIQUES FOR PARTIAL DIFFERENTIAL EQUATIONS
Authors: MÜLLER T. G. , TIMMER J.
Published: July 2004

Many physical systems exhibiting nonlinear spatiotemporal dynamics can be modeled by partial differential equations. Although information about the physical properties for many of these systems is available, normally not all dynamical parameters are known and, therefore, have to be estimated from experimental data. We analyze two prominent approaches to solve this problem and describe advantages and disadvantages of both methods. Specifically, we focus on the dependence of the quality of the parameter estimates with respect to noise and temporal and spatial resolution of the measurements.
RECONSTRUCTION OF THE DETERMINISTIC DYNAMICS OF STOCHASTIC SYSTEMS
Authors: SIEFERT M. , PEINKE J.
Published: July 2004

We show that based on the mathematics of Markov processes and particularly based on the definition of Kramers–Moyal coefficients, it is possible to estimate the deterministic part of the dynamics for a broad class of nonlinear noisy systems. In particular, we show that for different kinds of noise perturbations, including non-Langevin force with finite correlation time and independent measurement noise, the deterministic part can be reconstructed.
RELIABILITY OF SPIKE TIMING IN A NEURON MODEL
Authors: CASADO J. M. , BALTANÁS J. P.
Published: July 2004

Recently, it has been shown experimentally [Mainen & Sejnowski, 1995] that, in contrast to the lack of precision in spike timing associated with flat (dc) stimuli, neocortical neurons of rats respond reliably to weak input fluctuations resembling synaptic activity. This has led authors to suggest that, in spite of the high variability of interspike intervals found in cortical activity, the mechanism of spike generation in neocortical neurons has a low level of intrinsic noise. In this work we approach the problem of spike timing by using the well-known FitzHugh–Nagumo (FHN) model of neuronal dynamics and find that here also, fluctuating stimuli allow a more reliable temporal coding than constant suprathreshold signals. This result is associated with the characteristics of a phenomenological stochastic bifurcation taking place in the noisy FHN model.
IDENTIFICATION OF RATE CONSTANTS AND NONOBSERVABLE ABSORPTION SPECTRA IN NONLINEAR BIOCHEMICAL REACTION DYNAMICS
Authors: MARAUN D. , HORBELT W. , RUST H. , TIMMER J. , HAPPERSBERGER H. P. , DREPPER F.
Published: July 2004

On analyzing data of biochemical reaction dynamics monitored by time-resolved spectroscopy, one faces the problem that the concentration time courses of the involved components are not directly observed, but the superposition of their absorption spectra. Furthermore the single spectra are often unknown, because the corresponding reagents cannot be isolated. We propose a method based on Bock's multiple shooting algorithm to estimate the rate constants and individual spectra simultaneously. Applying this procedure to a biochemical reaction we identify the specific rate constants characterizing the reaction dynamics as well as the nonobservable absorption spectra. The results lead to a better understanding of the kinetics of a novel modification reaction which was used as trapping reaction in disulfide bond mediated protein folding reactions.
ESTIMATION OF MODEL PARAMETERS FROM TIME SERIES BY OPCL AUTO-SYNCHRONIZATION
Authors: GROSU IOAN
Published: July 2004

OPCL autosynchronization ([1997] Phys. Rev.E56, 3709–3711) is used for determination of parameters in 1-D models. Numerical results are given for noisy Duffing and logistic systems. The proposed algorithm works also for models that contain parameters nonlinearly. Numerical results show that the error function has a global minimum.
THE UNSCENTED KALMAN FILTER, A POWERFUL TOOL FOR DATA ANALYSIS
Authors: SITZ A. , SCHWARZ U. , KURTHS J.
Published: July 2004

We present a derivation of the unscented Kalman filter (UKF) as an approximation to the optimal Bayesian filter equations. The potentials of the UKF are then demonstrated for the problem of simultaneous estimation of states and parameters from noise corrupted data of nonlinear dynamical systems. The UKF even works for the chaotic Chua system which includes nondifferentiable terms.
SURROGATE-BASED HYPOTHESIS TEST WITHOUT SURROGATES
Authors: THIEL MARCO , ROMANO M. CARMEN , SCHWARZ UDO , KURTHS JÜRGEN , TIMMER JENS
Published: July 2004

Fourier surrogate data are artificially generated time series, that — based on a resampling scheme — share the linear properties with an observed time series. In this paper we study a statistical surrogate hypothesis test to detect deviations from a linear Gaussian process with respect to asymmetry in time (Q-statistic). We apply this test to a Fourier representable function and obtain a representation of the asymmetry in time of the sample data, a characteristic for nonlinear processes, and the significance in terms of the Fourier coefficients. The main outcome is that we calculate the expected value of the mean and the standard deviation of the asymmetries of the surrogate data analytically and hence, no surrogates have to be generated. To illustrate the results we apply our method to the saw tooth function, the Lorenz system and to measured X-ray data of Cygnus X-1.
ACTIVE DEFORMABLE MODELS USING DENSITY ESTIMATION
Authors: ABD-ALMAGEED WAEL , SMITH CHRISTOPHER E.
Published: July 2004

This paper introduces a new approach to active deformable models. The paper starts with a brief review of the relevant approaches. We then use the Expectation Maximization and Parzen Window techniques to develop a more robust formulation for pressure snakes. The generic nature of the proposed model allows it to perform well on complex colored images. We show, by several examples, the enhanced performance of the snake under the new formulation, compared to the performance of other known snake formulations.
DEFORMABLE MESH FOR AUTOMATED SURFACE EXTRACTION FROM NOISY IMAGES
Authors: TOHKA JUSSI , MYKKÄNEN JOUNI M.
Published: July 2004

Surface extraction from noisy volumetric images is a problem commonly encountered in medical image analysis. Deformable surface models can, in principle, solve the problem in an automatic manner. However, it is often essential that a reasonably close initialization and good parameter values for deformable models are provided. In this paper, novel algorithms for global minimization of the energy of deformable meshes are presented. We demonstrate that global optimization by these algorithms reduces the sensitivity of the deformable mesh to its initialization and its parameter values. Consequently, it becomes easier to automate the initialization process and the selection of parameter values. As the second contribution, the internal energy function is derived in a novel way in the framework of deformable surface models. The construction of the internal energy in this way features a simple way to derive the variants of our global optimization algorithm. The experiments with synthetic images are performed to compare variants of the proposed optimization algorithm. Also, we present a practical application of our deformable model to automatic segmentation of positron emission tomography images.
INTER-FRAME PREDICTION OF MEDICAL AND VIDEOPHONE SEQUENCES: A DEFORMABLE TRIANGLE-BASED APPROACH
Authors: YAZDI MEHRAN , ZACCARIN ANDRE
Published: July 2004

Motion compensation using deformable triangle patches has been successfully used for low bit rate coding of videophone sequences. They were also shown to be particularly efficient for interframe coding of MRI sequences, for which the difference between image slices can be well modeled by locally affine deformations. Regular triangular meshes were used in previous works. In this paper, we present a quadtree decomposition algorithm to generate a triangle mesh for which smaller triangles are used in image areas where the motion or deformation is more complex. Grid points are recursively added to areas where the reduction in prediction error is more significant. Results show that using variable size triangular patches increases the PSNR of the motion-compensated image while reducing the number of grid points when compared to a regular triangular mesh.
Inflammation and Cancer V. Chronic pancreatitis and pancreatic cancer
Authors: Whitcomb David C.
Published: July 2004

Pancreatic inflammation appears to increase the risk of pancreatic cancer. This observation is striking in the hereditary pancreatitis kindreds but also occurs in alcoholic, idiopathic, and tropical chronic pancreatitis and cystic fibrosis. However, the mutations associated with hereditary pancreatitis or cystic fibrosis are not found in sporadic pancreatic adenocarcinomas, suggesting that the effects are indirect by causing recurrent pancreatitis and chronic inflammation. The process of mutation accumulation and clonal expansion that is required for development of invasive pancreatic adenocarcinoma must therefore be accelerated in chronic pancreatitis to account for the high incidence of pancreatic cancer in these patients.
Protective effect of endogenous PPARγ against acute gastric mucosal lesions associated with ischemia-reperfusion
Authors: Wada Koichiro , Nakajima Atsushi , Takahashi Hirokazu , Yoneda Masato , Fujisawa Nobutaka , Ohsawa Emi , Kadowaki Takashi , Kubota Naoto , Terauchi Yasuo , Matsuhashi Nobuyuki , Saubermann Lawrence J. , Nakajima Noriko , Blumberg Richard S.
Published: July 2004

Acute gastric mucosal lesions (AGMLs) are an important cause of gastrointestinal bleeding. Herein, we demonstrate that peroxisome proliferator-activated receptor-γ (PPARγ), a member of a nuclear receptor family, functions as an endogenous anti-inflammatory pathway in a murine model of AGML induced by ischemia-reperfusion (I/R). Treatment with specific PPARγ ligands such as BRL-49653, pioglitazone, or troglitazone was examined in a model of AGML induced by I/R. PPARγ-deficient and wild-type mice were also examined for their response to I/R in stomach. Specific PPARγ ligands exhibited dramatic and rapid protection against AGML formation associated with I/R in mice in a dose-dependent manner. In contrast, the AGML induced by I/R in PPARγ-deficient mice was more severe than that observed in wild-type mice. Administration of the PPARγ ligand significantly inhibited the upregulation of TNF-α, ICAM-1, inducible nitric oxide synthase, apoptosis, and nitrotyrosine formation induced by I/R in the stomach. These data indicate that an endogenous pathway associated with PPARγ plays an important role in the pathogenesis of I/R-associated injury in the stomach.
Time-dependent remodeling of transmural architecture underlying abnormal ventricular geometry in chronic volume overload heart failure
Authors: Ashikaga Hiroshi , Omens Jeffrey H. , Covell James W.
Published: July 2004

To test the hypothesis that the abnormal ventricular geometry in failing hearts may be accounted for by regionally selective remodeling of myocardial laminae or sheets, we investigated remodeling of the transmural architecture in chronic volume overload induced by an aortocaval shunt. We determined three-dimensional finite deformation at apical and basal sites in left ventricular anterior wall of six dogs with the use of biplane cineradiography of implanted markers. Myocardial strains at end diastole were measured at a failing state referred to control to describe remodeling of myofibers and sheet structures over time. After 9 ± 2 wk (means ± SE) of volume overload, the myocardial volume within the marker sets increased by >20%. At 2 wk, the basal site had myofiber elongation (0.099 ± 0.030; P < 0.05), whereas the apical site did not [ P = not significant (NS)]. Sheet shear at the basal site increased progressively toward the final study (0.040 ± 0.003 at 2 wk and 0.054 ± 0.021 at final; both P < 0.05), which contributed to a significant increase in wall thickness at the final study (0.181 ± 0.047; P < 0.05), whereas the apical site did not ( P = NS). We conclude that the remodeling of the transmural architecture is regionally heterogeneous in chronic volume overload. The early differences in fiber elongation seem most likely due to a regional gradient in diastolic wall stress, whereas the late differences in wall thickness are most likely related to regional differences in the laminar architecture of the wall. These results suggest that the temporal progression of ventricular remodeling may be anatomically designed at the level of regional laminar architecture.
Periods of intermittent hypoxic apnea can alter chemoreflex control of sympathetic nerve activity in humans
Authors: Cutler Michael J. , Swift Nicolette Muenter , Keller David M. , Wasmund Wendy L. , Burk John R. , Smith Michael L.
Published: July 2004

Obstructive sleep apnea is associated with sustained elevation of muscle sympathetic nerve activity (MSNA) and altered chemoreflex control of MSNA, both of which likely play an important role in the development of hypertension in these patients. Additionally, short-term exposure to intermittent hypoxic apneas can produce a sustained elevation of MSNA. Therefore, we tested the hypothesis that 20 min of intermittent hypoxic apneas can alter chemoreflex control of MSNA. Twenty-one subjects were randomly assigned to one of three groups (hypoxic apnea, hypercapnic hypoxia, and isocapnic hypoxia). Subjects were exposed to 30 s of the perturbation every minute for 20 min. Chemoreflex control of MSNA was assessed during baseline, 1 min posttreatment, and every 15 min throughout 180 min of recovery by the MSNA response to a single hypoxic apnea. Recovery hypoxic apneas were matched to a baseline hypoxic apnea with a similar nadir oxygen saturation. A significant main effect for chemoreflex control of MSNA was observed after 20 min of intermittent hypoxic apneas ( P < 0.001). The MSNA response to a single hypoxic apnea was attenuated 1 min postexposure compared with baseline ( P < 0.001), became augmented within 30 min of recovery, and remained augmented through 165 min of recovery ( P < 0.05). Comparison of treatment groups revealed no differences in the chemoreflex control of MSNA during recovery ( P = 0.69). These data support the hypothesis that 20 min of intermittent hypoxic apneas can alter chemoreflex control of MSNA. Furthermore, this response appears to be mediated by hypoxia.
Saturation of high-frequency oscillations of R-R intervals in healthy subjects and patients after acute myocardial infarction during ambulatory conditions
Authors: Kiviniemi Antti M. , Hautala Arto J. , Seppänen Tapio , Mäkikallio Timo H. , Huikuri Heikki V. , Tulppo Mikko P.
Published: July 2004

This study was designed to assess the relationship between R-R interval length and heart rate (HR) variability in healthy subjects and patients after an acute myocardial infarction (AMI). Twenty-four-hour ambulatory ECG recordings were obtained for 76 healthy subjects and 82 post-AMI patients. The high-frequency (HF, 0.15–0.4 Hz) spectral power of R-R intervals was analyzed in 5-min sequences over 24 h and plotted as a function of the corresponding mean R-R interval length. Quadratic regression model was used to study the relationship between R-R interval length and HF power. If a distinct deflection point (R-R0) occurred in the quadratic regression ( r > 0.50) model before maximum R-R interval, indicating the plateau of HF power, the relationship between R-R interval and HF power was defined as saturated. Otherwise, the relationship was defined as linear ( r > 0.50) or low correlated ( r > 0.50). The relationship was saturated in 35, linear in 38, and low correlated in 3 healthy subjects. In post-AMI patients, the relationship was saturated in 9 subjects, linear in 44 subjects, and low correlated in 29 patients. The HF power analyzed from the 24-h period did not differ between the saturated and linear groups, but when analyzed from the linear portion only, HF spectral power was smaller in the linear than the saturated group both among healthy subjects ( P < 0.05) and post-AMI patients ( P < 0.05). Saturation of the HF oscillations of R-R intervals is a common phenomenon in healthy subjects and also present in post-AMI patients during ambulatory conditions. This saturation effect may bias the quantification of cardiac vagal function when HR variability is analyzed from Holter recordings.
Novel targets of ANG II regulation in mouse heart identified by serial analysis of gene expression
Authors: Schwartz Faina , Duka Arvi , Duka Irena , Cui Jing , Gavras Haralambos
Published: July 2004

Although the central role of ANG II in cardiovascular homeostasis is well appreciated, the molecular circuitry of its many actions is not completely understood. With the use of serial analysis of gene expression to assess global transcriptional changes in the heart of mice after continuous 7-day ANG II administration, we identified patterns of gene expression indicative of cardiac remodeling, including coordinate regulation of genes previously described in a context of processes associated with hypertrophy and fibrosis. In addition, we discovered several novel ANG II targets, including characterized genes of known function, recently annotated genes of unknown function, and the putative genes not yet present in current databases. The serial analysis of gene expression approach to assess the role of ANG II presented in this report provides new venues for inquiries into ANG II-mediated cardiac function.
Seasonality of dihydropyridine receptor binding in the heart of an anoxia-tolerant vertebrate, the crucian carp (Carassius carassiusL.)
Authors: Vornanen Matti , Paajanen Vesa
Published: July 2004

Prolonged anoxia tolerance of facultative anaerobes is based on metabolic depression and thus on controlled reduction of energy-utilizing processes. One proposed survival mechanism is the closing of ion channels to decrease energetic cost of ion pumping (Hochachka PW. Science 231: 234–241, 1986). To test this hypothesis, the involvement of L-type Ca2+channels in seasonal anoxia tolerance of the vertebrate heart was examined by determining the number of [ methyl-3H]PN200–110 (a ligand of L-type Ca2+channel α-subunit) binding sites of the cardiac tissue and the density of Ca2+current in ventricular myocytes of an anoxia-resistant fish species, the crucian carp. In their natural environment, the fish were exposed for >3 mo of hypoxia (O2<2.5 mg/l) followed by almost 8 wk of anoxia that resulted in abrupt depletion of cardiac glycogen stores in late spring. Unexpectedly, however, the number of [ methyl-3H]PN200–110 binding sites did not decline in hypoxia/anoxia as predicted by the channel arrest hypothesis but remained constant for most of the year. However, in early summer, the number of [ methyl-3H]PN200–110 binding sites doubled for a period of ∼2 mo, which functionally appeared as a 74% larger Ca2+current density. Thus the anoxia tolerance of the carp heart cannot be based on downregulation of Ca2+channel units in myocytes but is likely to depend on suppressed heart rate, i.e., regulation of the heart at the systemic level, and direct depressive effects of low temperature on Ca2+current to achieve savings in cardiac work load and ion pumping. The summer peak in the number of functional Ca2+channels indicates a short period of high cardiac activity possibly associated with reproduction and active perfusion of tissues after the winter stresses.
Differential gene expression associated with euryhalinity in sea bream (Sparus sarba)
Authors: Deane Eddie E. , Woo Norman Y. S.
Published: July 2004

Certain fish have the remarkable capability of euryhalinity, being able to withstand large variations in salinity for indefinite periods. Using the highly euryhaline species, silver sea bream ( Sparus sarba), as an experimental model, some of the molecular processes involved during ion regulation (Na+-K+-ATPase), cytoprotection [heat shock protein (hsp) 70], and growth (somatotropic axis) were studied. To perform these studies, seven key genes involved in these processes were cloned, and the tissue-specific expression profiles in fish adapted to salinities of 6 parts per thousand (ppt; hypoosmotic), 12 ppt (isoosmotic), 33 ppt (seawater), and 50 ppt (hypersaline) were studied. In gills, the transcriptional and translational expression profiles of Na+-K+-ATPase α- and β-subunit genes were lowest in isoosmotic-adapted fish, whereas in kidneys the expression of the β-subunit increased in seawater- and hypersaline-adapted groups. The hsp70 multigene family, comprising genes coding for heat shock cognate ( hsc70), inducible heat shock protein ( hsp70), and a heat shock transcription factor ( hsf1), was found to be highly upregulated in gills of seawater- and hypersaline-adapted fish. In liver, hsc70 expression was lowest in isoosmotic groups, and in kidneys the hsp70 multigene family remained unchanged over the salinity range tested. The regulation of the somatotropic axis was studied by measuring pituitary growth hormone expression and liver IGF-I expression in salinity-adapted fish. The expression amounts of both genes involved in the somatotropic axis were highest in fish maintained at an isoosmotic salinity. The results of this study provide new information on key molecular processes involved in euryhalinity of fish.
Large lesions in the pre-Bötzinger complex area eliminate eupneic respiratory rhythm in awake goats
Authors: Wenninger J. M. , Pan L. G. , Klum L. , Leekley T. , Bastastic J. , Hodges M. R. , Feroah T. R. , Davis S. , Forster H. V.
Published: July 2004

In awake goats, 29% bilateral destruction of neurokinin-1 receptor-expressing neurons in the pre-Bötzinger complex (pre-BötzC) area with saporin conjugated to substance P results in transient disruptions of the normal pattern of eupneic respiratory muscle activation (Wenninger JM, Pan LG, Klum L, Leekley T, Bastastic J, Hodges MR, Feroah T, Davis S, and Forster HV. J Appl Physiol 97: 1620–1628, 2004). Therefore, the purpose of these studies was to determine whether large or total lesioning in the pre-BötzC area of goats would eliminate phasic diaphragm activity and the eupneic breathing pattern. In awake goats that already had 29% bilateral destruction of neurokinin-1 receptor-expressing neurons in the pre-BötzC area, bilateral ibotenic acid (10 μl, 50 mM) injection into the pre-BötzC area resulted in a tachypneic hyperpnea that reached a maximum (132 ± 10.1 breaths/min) ∼30–90 min after bilateral injection. Thereafter, breathing frequency declined, central apneas resulted in arterial hypoxemia (arterial Po2 ∼40 Torr) and hypercapnia (arterial Pco2 ∼60 Torr), and, 11 ± 3 min after the peak tachypnea, respiratory failure was followed by cardiac arrest in three airway-intact goats. However, after the peak tachypnea in four tracheostomized goats, mechanical ventilation was initiated to maintain arterial blood gases at control levels, during which there was no phasic diaphragm or abdominal muscle activity. When briefly removed from the ventilator (∼90 s), these goats became hypoxemic and hypercapnic. During this time, minimal, passive inspiratory flow resulted from phasic abdominal muscle activity. We estimate that 70% of the neurons within the pre-BötzC area were lesioned in these goats. We conclude that, in the awake state, the pre-BötzC is critical for generating a diaphragm, eupneic respiratory rhythm, and that, in the absence of the pre-BötzC, spontaneous breathing reflects the activity of an expiratory rhythm generator.
Training-induced changes in muscle CSA, muscle strength, EMG, and rate of force development in elderly subjects after long-term unilateral disuse
Authors: Suetta Charlotte , Aagaard Per , Rosted Anna , Jakobsen Ane K. , Duus Benn , Kjaer Michael , Magnusson S. Peter
Published: July 2004

The ability to develop muscle force rapidly may be a very important factor to prevent a fall and to perform other tasks of daily life. However, information is still lacking on the range of training-induced neuromuscular adaptations in elderly humans recovering from a period of disuse. Therefore, the present study examined the effect of three types of training regimes after unilateral prolonged disuse and subsequent hip-replacement surgery on maximal muscle strength, rapid muscle force [rate of force development (RFD)], muscle activation, and muscle size. Thirty-six subjects (60–86 yr) were randomized to a 12-wk rehabilitation program consisting of either 1) strength training (3 times/wk for 12 wk), 2) electrical muscle stimulation (1 h/day for 12 wk), or 3) standard rehabilitation (1 h/day for 12 wk). The nonoperated side did not receive any intervention and thereby served as a within-subject control. Thirty subjects completed the trial. In the strength-training group, significant increases were observed in maximal isometric muscle strength (24%, P < 0.01), contractile RFD (26–45%, P < 0.05), and contractile impulse (27–32%, P < 0.05). No significant changes were seen in the two other training groups or in the nontrained legs of all three groups. Mean electromyogram signal amplitude of vastus lateralis was larger in the strength-training than in the standard-rehabilitation group at 5 and 12 wk ( P < 0.05). In contrast to traditional physiotherapy and electrical stimulation, strength training increased muscle mass, maximal isometric strength, RFD, and muscle activation in elderly men and women recovering from long-term muscle disuse and subsequent hip surgery. The improvement in both muscle mass and neural function is likely to have important functional implications for elderly individuals.
Functional evaluation of human ClC-2 chloride channel mutations associated with idiopathic generalized epilepsies
Authors: Niemeyer María Isabel , Yusef Yamil R. , Cornejo Isabel , Flores Carlos A. , Sepúlveda Francisco V. , Cid L. Pablo
Published: July 2004

The ClC-2 Cl− channel has been postulated to play a role in the inhibitory GABA response in neurons or to participate in astrocyte-dependent extracellular electrolyte homeostasis. Three different mutations in the CLCN2 gene, encoding the voltage-dependent homodimeric ClC-2 channel, have been associated with idiopathic generalized epilepsy (IGE). We study their function in vitro by patch clamp and confocal microscopy in transiently transfected HEK-293 cells. A first mutation predicts a premature stop codon (M200fsX231). An altered splicing, due to an 11-bp deletion in intron 2 (IVS2-14del11), predicts exon 3 skipping (Δ74–117). A third is a missense mutation (G715E). M200fsX231 and Δ74–117 are nonfunctional and do not affect the function of the normal (wild type, WT) channel. Neither M200fsX231 nor Δ74–117 reach the plasma membrane. Concerning the IVS2-14del11 mutation, we find no difference in the proportion of exon-skipped to normally spliced mRNA using a minigene approach and, on this basis, predict no alteration in channel expression in affected individuals. G715E has voltage dependence and intracellular Cl− dependence indistinguishable from WT channels. ClC-2 channels are shown to be sensitive to intracellular replacement of ATP by AMP, which accelerates the opening and closing kinetics. This effect is diminished in the G715E mutant and not significant in WT+G715E coexpression. We do not know whether, in a situation of cellular ATP depletion, this might become pathological in individuals carrying the mutation. We postulate that loss of function mutation M200fsX231 of ClC-2 might contribute to the IGE phenotype through a haploinsufficiency mechanism.
Tissue plasminogen activator and neuroserpin are widely expressed in the human central nervous system
Authors: Kulla Andres , Simisker Aadu , Sirén Vappu , Lawrence Daniel , Asser Toomas , Vaheri Antti , Teesalu Tambet
Published: July 2004

Tissue plasminogen activator (tPA) is increasingly recognized to play important roles in various physiological and pathological processes in the central nervous system (CNS). Much of the data on the involvement of plasminogen activators in neurophysiology and -pathology have been derived from studies on experimental animals. We have now performed a systematic characterization of the expression of tPA and its inhibitor, neuroserpin, in normal human CNS. Brain and spinal cord samples from 30-36 anatomic locations covering all major brain regions were collected at 9 autopsies of donors with no neurological disease. Tissues were embedded in paraffin and tissue arrays were constructed. In two cases parallel samples were snap-frozen for biochemical analysis. Expression and activity profiling of tPA and neuroserpin were performed by immunohistochemistry, in situ hybridization, immunocapture and zymography assays. In the adult CNS, tPA was expressed at the mRNA and protein levels in many types of neurons, in particular in thalamus, cortex of cerebellum, pontine nuclei, neocortex, limbic system, and medulla oblongata. Interestingly, tPA was often co-expressed with its CNS inhibitor, neuroserpin. Despite overlapping expression of tPA and neuroserpin, zymography and immunocapture assays demonstrated that human neural tissue is a rich source of active tPA. Our analysis documents a detailed map of expression of tPA and its inhibitor in the human CNS and is compatible with the view that tPA is a key player in CNS physiology and pathology.
Activation of fibrinolysis in the pericardial cavity after cardiopulmonary bypass
Authors: Ismail Mohamed , Kalmar Peter , von Knobelsdorff Georg , Marx Guy , Khalil Philipe
Published: July 2004

Aprotinin is frequently administered systemically in patients undergoing cardiopulmonary bypass to preserve platelet function and ameliorate excessive activation of fibrinolysis. More recently, aprotinin topically applied in the pericardial cavity was also found to improve postoperative blood loss. However, platelet activation was not reduced locally during surgery. Hence, we investigated in the present prospective, in a randomized double-blind trial, the intra- and early postoperative state of systemic and local fibrinolytic activity, and whether topically administered aprotinin acts as an antifibrinolytic and therefore improves local hemostasis. Patients undergoing elective coronary artery bypass grafting were divided in two groups containing 22 patients each. Both, group I and II patients received highdose aprotinin (6.0 × 106 kallikrein inhibitor units (KIU)) systemically. Before resuming extracorporeal circulation (ECC), either 1.0 × 106 KIU aprotinin (group I) or vehicle solution (group II) was applied into the pericardial cavity. Plasminogen, α2-antiplasmin, plasmin-α2-antiplasmin complex, plasminogenactivator-inhibitor type-1 and D-dimers were measured in the pericardial cavity and systemic circulation immediately before resuming extracorporeal circulation (ECC), and at 1 h and 4 h postoperatively. The local fibrinolytic activity was found to significantly exceed that measured in the systemic circulation over time, whether ot not they received aprotinin into the thoracic wound surface. Furthermore, evidence was provided that topically applied aprotinin reduces not only the local fibrinolytic activity but also the postoperative blood loss significantly by 33% which demonstrates the clinical relevance. The local activation of fibrinolysis seems to play an important role in blood loss after cardiopulmonary bypass. Therefore in fibrinolysis and blood coagulation the surgeon should not only consider what happens in the systemic circulation but also on a local level.
Recombinant urokinase for restoration of patency in occluded central venous access devices
Authors: Deitcher Steven , Mullane Kathleen , Jaff Michael , Firszt Carolyn , Schulz Gregory , Schuerr Debra , Schwartz Lewis , Mouginis Tamyra , Barton R. , Haire William
Published: July 2004

The interval occlusion of central venous access devices (CVADs) remains a significant clinical problem, often requiring re-intervention for catheter exchange or replacement.The purpose of this Phase 3, multi-center, double-blinded study was to test the hypothesis that instillation of recombinant urokinase (r-UK) 5000 IU/ml is superior to placebo in restoring total catheter patency to an unselected cohort of occluded CVADs. After obtaining informed consent, adult and pediatric patients with occluded, non-hemodialysis CVADs of any duration or type were randomized (2 : 1) to receive either r-UK 5000 IU/ml or placebo instilled into all occluded lumens of their catheter. Catheter function was assessed at 5, 15 and 30 min after the first instillation. If the catheter remained occluded after 30 min, a second dose was instilled with repeat assessments at 5, 15 and 30 min.The primary efficacy variable was the restoration of catheter function to all treated lumens (i.e., total catheter patency) after one or two instillations. Catheters that were not successfully recanalized after two instillations were allowed to receive up to two instillations of open-label r-UK administered in the same manner.The primary safety variable was the occurrence of hemorrhagic and non-hemorrhagic events within 72 hr after instillation. A total of 180 patients were enrolled at 43 sites in the United States and Canada. Most patients were adults, although 20% were ≤18 years of age. CVAD types included totally implanted subcutaneous ports (45%), PICC lines (26%), non-tunneled percutaneous catheters (18%), and tunneled percutaneous catheters (10%). All CVADs were occluded by virtue of their inability to withdraw blood (withdrawal occlusion). Additionally, 32% of catheters were completely dysfunctional as blood could not be withdrawn and fluids could not be infused (total occlusion). Analysis of the results showed that r-UK was significantly better than placebo in restoring catheter function (54% versus 30%, p = 0.002). There were no major hemorrhagic events within 72 hr after up to four r-UK instillations, and the incidence of non-hemorrhagic events was similar among the r-UK and placebo groups. In conclusion, r-UK is superior to placebo in restoring total catheter patency to occluded CVADs. In patients with occluded CVADs, intra-catheter thrombolysis can restore patency and may obviate the need for catheter replacement.
Neutrophil function in the healing wound: adding insult to injury?
Authors: Dovi Julia , Szpaderska Anna , DiPietro Luisa
Published: July 2004

Cells of the innate immune system, including neutrophils and macrophages, are a highly visible component of normal wound healing in adult mammals. The role of inflammatory cells in the healing wound has been widely investigated, and evidence for both positive and negative influences exists. Several recent investigations support the emerging paradigm that robust inflammation is detrimental to wound closure. This developing information suggests that the functional role of inflammatory cells in wound healing must be reevaluated.
Genetic and environmental influences on the fibrinolytic system: a twin study
Authors: Victor Anja , Adams Petra , Erbes Hilde , Hafner Gerd , Lackner Karl , Hoehler Thomas , Peetz Dirk
Published: July 2004

The determination of heritability is a key issue to assess the predictive power of polymorphisms for disease in clinical studies. The aim of this study was to determine the heritability of proteins and activation markers of the fibrinolytic system in a large cohort of healthy twins. Heritability was calculated as 0.76 for thrombin activatable fibrinolysis inhibitor (TAFI), 0.44 for plasminogen activator inhibitor-1 (PAI-1), and 0.43 for tissue plasminogen activator. No significant genetic influence was observed for α2-antiplasmin-plasmin-complex and D-dimer. Heritability explained by single gene polymorphisms was 25.2% for TAFI 505G>A, 31.5% for 1542C>G, and 50.0% for combination of both. The influence on TAFI levels of 1542C>G (CC→GG, median: −280.5%) was considerably stronger than that of 505G>A (GG→AA, median: +49.3%) and in both cases there seems to be a dose-response relationship. Significant environmental influences on TAFI levels were observed for combined interaction terms (age*sex and bmi*sex). The PAI-1 4G/5G polymorphism explained 56.4% of the calculated heritability. The genetic variables accounting for the 43% heritability of tPA remain unknown. Our data show that the production of several key components of the fibrinolytic system is strongly genetically determined. This genetic influence is accounted for in large part but not completely by a limited number of polymorphisms within the respective genes associated with plasma levels of the gene products.
Characterization of plasminogen variants in healthy subjects and plasminogen mutants in patients with inherited plasminogen deficiency by isoelectric focusing gel electrophoresis
Authors: Tefs Katrin , Georgieva Maria , Seregard Stefan , Tait Campbell , Luchtman-Jones Lori , Ziegler Maike , Hügle Boris , Schuster Volker
Published: July 2004

Plasmin(ogen) plays an important role in fibrinolysis and wound healing. Severe hypoplasminogenemia has recently been linked to ligneous conjunctivitis. Plasminogen (plg) is known as a polymorphic protein and most of these variants have been identified using isoelectric focusing (IEF) gel electrophoresis. Here, we studied common plg variants from healthy subjects and plg mutants from three patients with hypoplasminogenemia and three subjects with dysplasminogenemia by molecular genetic analysis and IEF. Analysis of 24 healthy subjects showed that subjects with the most common IEF plg phenotype A (n = 12) were homozygous for aspartate at position 453 (453D), while both subjects with IEF plg phenotype B were homozygous for asparagine at this position (453N). Subjects with IEF plg phenotype AB (n = 10) were compound-heterozygous for 453D/453N. Three patients with severe hypoplasminogenemia and different plg gene mutations exhibited characteristic “abnormal” IEF band patterns when compared with IEF plg phenotypes A and B. In all heterozygous family members the observed IEF plg phenotype was derived from the wild type plg molecule only, probably due to low concentration of the mutant plg molecule in plasma. In contrast, in three unrelated subjects with heterozygous dysplasminogenemia an equal “mixture” of wild type and mutant plg was found by IEF analysis. In conclusion, plg phenotyping by IEF in combination with molecular analysis of the plg gene seems to be a useful method for characterization of plg variants and mutants.
Platelet hyperreactivity in hemodialysis patients with frequently occluded vascular access
Authors: Chou Kang-Ju , Jan Chung-Ren , Lee Po-Tsang , Chen Chien-Liang , Chung Hsiao-Min , Hwang Yueh-Yen , Chou Jing-Dung , Fang Hua-Chang
Published: July 2004

It is known that thrombosis is a leading cause of vascular access failure and that the formation of thrombus requires platelets. The activation of platelets induces the increase in intracellular Ca2+ levels ([Ca2+]i) leading to aggregation and thrombosis. We compared the platelet [Ca2+]i
before and after stimulation between the patients with and without easily occluded vascular access. Our study included two groups of hemodialysis patients. Group 1 consisted of 21 patients who had received chronic hemodialysis therapy for more than 6 months. They had had more than three events (including three) of vascular access failures during the past year. Group 2 consisted of 21 hemodialysis patients with age, sex, and diabetes mellitus matched who had never suffered from any event of vascular access failure. We measured the basal and stimulated platelet [Ca2+]i
after stimulation with 1 U/ml thrombin, 1 µM arachidonic acid, 1 µM platelet activation factor (PAF), and 10 µM adenosine diphosphate (ADP), respectively. Our results showed that in Ca2+-containing media, there was no significant differences in the basal [Ca2+]i
, but the maximal increases of [Ca2+]i
of platelets were higher (p <0.05) in group 1 than in group 2 after stimulating with PAF and ADP, but not with thrombin and arachidonic acid. We concluded that the causes for the susceptibility of some hemodialysis patients to vascular access occlusion were multifactorial. In addition to previously reported plasma factors, there was a subgroup of patients who showed greater elevations of agonists stimulated platelet intracellular calcium levels.
Variable extent of clopidogrel responsiveness in patients after coronary stenting
Authors: Schnurr Axel , Bonz Andreas , Porsche Christian , Obergfell Achim , Lengenfelder Björn , Walter Ulrich , Eigenthaler Martin , Grossmann Ralf , Sokolova Olga
Published: July 2004

Clopidogrel is an effective and specific inhibitor of ADP-induced platelet aggregation. After metabolic activation, the active clopidogrel metabolite irreversibly impairs the human platelet P2Y12 ADP receptor. Gialpha-protein activation and inhibition of vasodilator-stimulated phosphoprotein (VASP) phosphorylation are two key elements of the P2Y12 receptor pathway suitable for quantitation of clopidogrel effects. So far, only limited data exist about a diminished responsiveness to clopidogrel and underlying possible mechanisms. We investigated clopidogrel effects in 57 patients after percutaneous coronary intervention and stent implantation by flow cytometry for the analysis of intracellular VASP phosphorylation. Patients were treated with a 300 mg clopidogrel loading dose, followed by 75 mg/day clopidogrel in combination with 100 mg/day aspirin. Samples were drawn after a median of 5 days of clopidogrel treatment. Considerable differences in the responsiveness to clopidogrel could be observed and it was shown that 17.5% (10/57) of the patients revealed an inadequate responsiveness to clopidogrel despite continuation of clopidogrel intake. Comparable amounts of Gialpha and VASP were found in two clopidogrel low-responding patients as well as in two responding patients. To exclude a molecular defect of P2Y12 ADP receptor, the P2Y12 receptor gene of eight clopidogrel treated patients (seven patients with inadequate responsiveness, one responder) was sequenced. We only found a single silent mutation in exon 2 at position 1828 (GA). We suggest that individual differences in clopidogrel metabolization could cause relevant variations in clopidogrel responsiveness despite the use of a 300 mg clopidogrel loading dose.
A comparative study of amyloid-beta (1-42) as a cofactor for plasminogen activation by vampire bat plasminogen activator and recombinant human tissue-type plasminogen activator
Authors: Schleuning Wolf-Dieter , Kruithof Egbert
Published: July 2004

The activity of both human tissue-type plasminogen activator (t-PA) and the PA from the saliva of the vampire bat, Desmodus rotundus, (DSPA) is critically dependent on the presence of a cofactor. The most efficient cofactor for both PAs is fibrin, but fibrinogen and amyloid beta peptides also have cofactor activities for human t-PA. Compared to t-PA, DSPA has a more stringent requirement for fibrin as a cofactor. The present study was undertaken to compare cofactor activities of amyloid beta 1-42 (Aβ1-42) for plasminogen activation by DSPA-α1 or by t-PA. The two PAs were incubated with different concentrations of glu-plasminogen, a chromogenic substrate for plasmin and 100 µg mL-1 of Aβ1-42, fibrinogen or fibrin as cofactor. Using the kinetic parameters directly determined from the chromogenic substrate conversion curves, we derived the relative efficacies of DSPA or t-PA in the presence of cofactor at the physiological plasminogen concentration of 2 µM. In the presence of fibrin, the activity of DSPA was comparable to that of t-PA and 23,270-fold higher than its activity without cofactor, whereas fibrin induced only a 248-fold increase in t-PA activity. The activity of DSPA with Aβ1-42 or fibrinogen as cofactor was 485-fold lower than its activity in the presence of fibrin, while for t-PA this difference was only 26-fold. The much lower activity of DSPA as compared to t-PA with Aβ1-42 or fibrinogen might lead to fewer side effects when used for the thrombolytic therapy of stroke.
Expression of therapeutic levels of factor VIII in hemophilia A mice using a novel adeno/adeno-associated hybrid virus
Authors: Gnatenko Dmitri , Wu Yong , Jesty Jolyon , Damon Andrea , Hearing Patrick , Bahou Wadie
Published: July 2004

We have generated an E1a/E1b/E3-deleted adeno/adeno-associated (Ad/AAV) hybrid virus driven by a small nuclear RNA (pHU1-1) promoter for expression of a B domain-deleted (Thr761-Asn1639) factor VIII transgene (FVIIIΔ761-1639). Productive replication of Ad/AAV/FVIIIΔ761-1639 in AAV repexpressing cells resulted in generation of monomeric and dimeric mini-adenoviral (mAd) replicative forms that retained the AAV integration elements (mAd/FVIIIΔ761-1639). In vitro studies using Ad/AAV/FVIIIΔ761-1639 generated ∼2-logs greater FVIII activity than mAd/FVIIIΔ761-1639. To determine its capacity for in vivo excision and/or genomic integration, Ad/AAV/FVIIIΔ761-1639 was injected by tail vein into three groups of hemophilia A mice (2 X 1011 vp [n = 3]; 4 X 1011 vp [n = 3]; 8 X 1011 vp [n = 3]), with clear concentration-dependent increase in FVIII activity (range 160-510 mU/ml; plasma activity 16% – 51% of normal). Peak activity was seen by Day (D) 5, with slow return to baseline by D28 (0.1 – 0.9% activity); in only 3/9 mice was loss of FVIII activity associated with development of anti-FVIII antibodies. Quantitative-PCR using genomic DNA isolated from D28 liver, spleen, heart, lungs, and kidney demonstrated the highest concentration in liver (∼10 genomes/ cell), with little to no organ toxicity at early (D5 or 6) or late (D28) post-infusion time points. There was no evidence for spontaneous transgene excision or genomic integration in vivo as evaluated by quantitative PCR and genomic blotting. These data establish (i) the feasibility and applicability of developing high-titer Ad/AAV hybrid viruses for FVIII delivery using a small cellular promoter, (ii) the potential utility of this virus for generation of “gutted” monomeric and dimeric mAD/FVIII retaining AAV integration elements, and (iii) that the development of strategies for regulated Rep68/78 co-expression may provide a novel approach for excision, integration, and long-term FVIII transgene expression.
A marriage of enhancement: fibrinolysis and conjunctive therapy
Authors: Welsh Robert , Armstrong Paul
Published: July 2004

Pharmacologic reperfusion of patients with acute ST segment elevation myocardial infarction is designed to achieve prompt high-quality reperfusion, prevent recurrent ischemia and reinfarction, maintain long-term patency, and to enhance patient survival and quality of life. Because monotherapy with fibrinolytics is by itself unable to achieve all of these objectives, antithrombotic, anti-platelet, and other novel agents are required. We discuss herein the role of unfractionated and enoxaparin, the potential added value of direct thrombin inhibitors, and the importance of aspirin. Despite the promise of glycoprotein IIb/IIIa inhibitors, risks associated with intracranial hemorrhage in the elderly have led to restraint in their application to broad populations. Facilitation of urgent percutaneous coronary intervention with combination reduced-dose fibrinolytic and glycoprotein IIb/IIIa inhibitors remains a promising potential future path. The future is likely to emphasize greater application of the already effective therapies at our disposal and the development of novel anti-platelet and anti-thrombin agents as well as those directed toward inflammation.