bluuebunny/crossref_metadata_2025 huggingface dataset:
Subnuclear compartmentalization of sequence-specific transcription factors and regulation of eukaryotic gene expression
Authors: Corry Gareth N , Underhill D Alan
Published: August 2005

To date, the majority of the research regarding eukaryotic transcription factors has focused on characterizing their function primarily through in vitro methods. These studies have revealed that transcription factors are essentially modular structures, containing separate regions that participate in such activities as DNA binding, protein–protein interaction, and transcriptional activation or repression. To fully comprehend the behavior of a given transcription factor, however, these domains must be analyzed in the context of the entire protein, and in certain cases the context of a multiprotein complex. Furthermore, it must be appreciated that transcription factors function in the nucleus, where they must contend with a variety of factors, including the nuclear architecture, chromatin domains, chromosome territories, and cell-cycle-associated processes. Recent examinations of transcription factors in the nucleus have clarified the behavior of these proteins in vivo and have increased our understanding of how gene expression is regulated in eukaryotes. Here, we review the current knowledge regarding sequence-specific transcription factor compartmentalization within the nucleus and discuss its impact on the regulation of such processes as activation or repression of gene expression and interaction with coregulatory factors.Key words: transcription, subnuclear localization, chromatin, gene expression, nuclear architecture.
Lsh, a guardian of heterochromatin at repeat elements
Authors: Muegge Kathrin
Published: August 2005

Lymphoid-specific helicase (Lsh) is a crucial factor for normal embryonic development; targeted deletion of Lsh is lethal. Lsh belongs to a family of chromatin-remodeling proteins and is closely associated with pericentromeric heterochromatin. Lsh deficiency leads to abnormal heterochromatin organization, with a loss of DNA methylation, and an altered pattern of histone-tail acetylation and methylation. As a functional consequence of perturbed heterochromatin, aberrant reactivation of parasitic retroviral elements in the genome and abnormal mitosis with amplified centrosomes and genomic instability were observed. Thus, Lsh is a major epigenetic regulator crucial for normal heterochromatin structure and function.Key words: chromatin, methylation, Lsh, DNA repeats.
Hypoxia and acidosis increase the secretion of catecholamines in the neonatal rat adrenal medulla: an in vitro study
Authors: Rico A. J. , Prieto-Lloret J. , Gonzalez C. , Rigual R.
Published: August 2005

Hypoxia elicits catecholamine (CA) secretion from the adrenal medulla (AM) in perinatal animals by acting directly on chromaffin cells. However, whether innervation of the AM, which in the rat occurs in the second postnatal week, suppresses this direct hypoxic response is the subject of debate. Opioid peptides have been proposed as mediators of this suppression. To resolve these controversies, we have compared CA-secretory responses with high external concentrations of K+ ([K+]e) and hypoxia in the AM of neonatal (1- to 2-day-old) and juvenile (14- or 15- and 30-day-old) rats subjected to superfusion in vitro. In addition, we studied the effect of hypercapnic acidosis on the CA-secretory responses in the AM during postnatal development and the possible interaction between acidic and hypoxic stimuli. Responses to high [K+]e were comparable at all ages, but responses to hypoxia and hypercapnic acidosis were maximal in neonatal animals. Suppression of the hypoxic response in the rat AM was not mediated by opioids, because their agonists did not affect the hypoxic CA response. The association of hypercapnic acidosis and hypoxia, mimicking the episodes of asphyxia occurring during delivery, generates a more than additive secretory response in the neonatal rat AM. Our data confirm the loss of the direct sensitivity to hypoxia of the AM in the initial weeks of life and demonstrate a direct response of neonatal AM to hypercapnic acidosis. The synergistic effect of hypoxia and acidosis would explain the CA outburst crucial for adaptation to extrauterine life observed in naturally delivered mammals.
Myomodulin IncreasesIhand Inhibits the Na/K Pump to Modulate Bursting in Leech Heart Interneurons
Authors: Tobin Anne-Elise , Calabrese Ronald L.
Published: August 2005

In the medicinal leech, a rhythmically active 14-interneuron network composes the central pattern generator for heartbeat. In two segmental ganglia, bilateral pairs of reciprocally inhibitory heart interneurons (oscillator interneurons) produce a rhythm of alternating bursts of action potentials that paces activity in the pattern-generating network. The neuropeptide myomodulin decreases the period of this bursting and increases the intraburst spike frequency when applied to isolated ganglia containing these oscillator interneurons. Myomodulin also decreases period, increases spike frequency, and increases the robustness of endogenous bursting in synaptically isolated (with bicuculline) oscillator interneurons. In voltage-clamp experiments using hyperpolarizing ramps, we identify an increase in membrane conductance elicited by myomodulin with the properties of a hyperpolarization-activated current. Voltage steps confirm that myomodulin indeed increases the maximum conductance of the hyperpolarization-activated current Ih. In similar experiments using Cs+to block Ih, we demonstrate that myomodulin also causes a steady offset in the ramp current that is not associated with an increase in conductance. This current offset is blocked by ouabain, indicating that myomodulin inhibits the Na/K pump. In current-clamp experiments, when Ihis blocked with Cs+, myomodulin decreases period and increases spike frequency of alternating bursting in synaptically connected oscillator interneurons, suggesting that inhibiting the Na/K pump modulates these burst characteristics. These observations indicate that myomodulin decreases period and increases spike frequency of endogenous bursting in synaptically isolated oscillator heart interneurons and alternating bursting of reciprocally inhibitory pairs of interneurons, at least in part, by increasing Ihand by decreasing the Na/K pump.
Constraining Compartmental Models Using Multiple Voltage Recordings and Genetic Algorithms
Authors: Keren Naomi , Peled Noam , Korngreen Alon
Published: August 2005

Compartmental models with many nonlinearly and nonhomogeneous distributions of voltage-gated conductances are routinely used to investigate the physiology of complex neurons. However, the number of loosely constrained parameters makes manually constructing the desired model a daunting if not impossible task. Recently, progress has been made using automated parameter search methods, such as genetic algorithms (GAs). However, these methods have been applied to somatically recorded action potentials using relatively simple target functions. Using a genetic minimization algorithm and a reduced compartmental model based on a previously published model of layer 5 neocortical pyramidal neurons we compared the efficacy of five cost functions (based on the waveform of the membrane potential, the interspike interval, trajectory density, and their combinations) to constrain the model. When the model was constrained using somatic recordings only, a combined cost function was found to be the most effective. This combined cost function was then applied to investigate the contribution of dendritic and axonal recordings to the ability of the GA to constrain the model. The more recording locations from the dendrite and the axon that were added to the data set the better was the genetic minimization algorithm able to constrain the compartmental model. Based on these simulations we propose an experimental scheme that, in combination with a genetic minimization algorithm, may be used to constrain compartmental models of neurons.
Environmental Enrichment Increases Paired-Pulse Depression in Rat Auditory Cortex
Authors: Percaccio Cherie R. , Engineer Navzer D. , Pruette Autumn L. , Pandya Pritesh K. , Moucha Raluca , Rathbun Daniel L. , Kilgard Michael P.
Published: August 2005

Temporal features are important for the identification of natural sounds. Earlier studies have shown that cortical processing of temporal information can be altered by long-term experience with modulated sounds. In a previous study, we observed that environmental enrichment dramatically increased the response of cortical neurons to single tone and noise burst stimuli in both awake and anesthetized rats. Here, we evaluate how enrichment influences temporal information processing in the auditory cortex. We recorded responses to repeated tones and noise bursts in awake rats using epidural evoked potentials and in anesthetized rats using microelectrodes. Enrichment increased the response of cortical neurons to stimuli presented at slow rates and decreased the response to stimuli presented at fast rates relative to controls. Our observation that enrichment substantially increased response strength and forward masking is consistent with earlier reports that long-term potentiation of cortical synapses is associated with increased paired-pulse depression. Enrichment also increased response synchronization at slow rates and decreased synchronization at fast rates. Paired-pulse depression increased within days of environmental enrichment and was restored to normal levels after return to standard housing conditions. These results are relevant to several clinical disorders characterized by abnormal gating of sensory information, including autism, schizophrenia, and dyslexia.
Sensory Neurons From Nf1 Haploinsufficient Mice Exhibit Increased Excitability
Authors: Wang Yue , Nicol G. D. , Clapp D. Wade , Hingtgen Cynthia M.
Published: August 2005

Neurofibromatosis type 1 (NF1) is a common genetic disorder characterized by tumor formation. People with NF1 also can experience more intense painful responses to stimuli, such as minor trauma, than normal. NF1 results from a heterozygous mutation of the NF1 gene, leading to decreased levels of neurofibromin, the protein product of the NF1 gene. Neurofibromin is a guanosine triphosphatase activating protein (GAP) for Ras and accelerates the conversion of active Ras-GTP to inactive Ras-GDP; therefore mutation of the NF1 gene frequently results in an increase in activity of the Ras transduction cascade. Using patch-clamp electrophysiological techniques, we examined the excitability of capsaicin-sensitive sensory neurons isolated from the dorsal root ganglia of adult mice with a heterozygous mutation of the Nf1 gene ( Nf1+/−), analogous to the human mutation, in comparison to wildtype sensory neurons. Sensory neurons from adult Nf1+/− mice generated a more than twofold higher number of action potentials in response to a ramp of depolarizing current as wild-type neurons. Consistent with the greater number of action potentials, Nf1+/− neurons had lower firing thresholds, lower rheobase currents, and shorter firing latencies than wild-type neurons. Interestingly, nerve growth factor augmented the excitability of wild-type neurons in a concentration-related manner but did not further alter the excitability of the Nf1+/− sensory neurons. These data clearly suggest that GAPs, such as neurofibromin, can play a key role in the excitability of nociceptive sensory neurons. This increased excitability may explain the painful conditions experienced by people with NF1.
Whisker Trimming Begun at Birth or on Postnatal Day 12 Affects Excitatory and Inhibitory Receptive Fields of Layer IV Barrel Neurons
Authors: Shoykhet Michael , Land Peter W. , Simons Daniel J.
Published: August 2005

In rats, whisker trimming during development leads to persistent alterations in the function of cortical barrel circuits and to behavioral deficits later in life. Here we examined how whisker trimming begun either at birth (P0) or on postnatal day 12 (P12), around the onset of whisking behavior, affects receptive fields of layer IV barrel neurons. All whiskers on the left face were trimmed for 40–45 days and then allowed to regrow fully. Extracellular single-unit recordings and controlled deflections of principal and adjacent whiskers (PW and AW, respectively), individually or in paired combinations, were used to assess excitatory and suppressive effects of neighboring whiskers on barrel neurons. Results indicate that whisker trimming both from P0 and P12 leads to enlarged excitatory and weakened inhibitory receptive fields in layer IV neurons. PW- and AW-evoked responses are larger in magnitude in trimmed than in control animals; AW-evoked responses are disproportionately affected, decreasing the spatial focus of barrel neurons. Deprivation after P12 accounts for ∼50% of the total effect observed in P0 trimmed animals. Suppressive interactions, evoked by two whiskers deflected in succession, are weaker in trimmed than in control animals. Suppressive caudal/rostral and ventral/dorsal gradients, however, seem unaffected by sensory deprivation. Thus the developmental period during which experience persistently modifies maturing barrel circuitry extends up to and likely beyond the onset of whisking behavior. Sensory deprivation during this time affects development of both excitatory and inhibitory receptive fields of barrel neurons and likely impairs cortical integration of sensory information from multiple whiskers.
Potassium Currents in Isolated Statocyst Neurons and RPeD1 in the Pond Snail,Lymnaea stagnalis
Authors: Sakakibara Manabu , Okuda Futoshi , Nomura Kazutoku , Watanabe Kenji , Meng Hongxu , Horikoshi Tetsuro , Lukowiak Ken
Published: August 2005

To begin to determine the underlying neural mechanisms of memory formation, we studied two different cell types that play important roles in different forms of associative learning in Lymnaea. Statocyst neurons (hair cells) mediate classical conditioning, whereas RPeD1 is a site of memory formation induced by operant conditioning of aerial respiration. Because potassium (K+) channels play a critical role in neuronal excitability, we initiated studies on these channels in the aforementioned neurons. Three distinct K+currents are expressed in the soma of both the hair cells and RPeD1. In hair cells and RPeD1, there is a fast activating and rapidly inactivating 4-aminopyridine (4-AP)-sensitive A current ( IA), a tetraethyl ammonium (TEA)-sensitive delayed rectifying current, which exhibits slow inactivation kinetics ( IKV), and a TEA- and 4-AP-insensitive Ca2+-dependent current ( ICa-K). In hair cells, the activation voltage of IA; its half-maximal steady-state activation voltage and its half-maximal steady-state inactivation were at more depolarized levels than in RPeD1. The time constant of recovery from IAinactivation was slightly faster in hair cells. IAin hair cells is also smaller in amplitude than in RPeD1 and is activated at more depolarized potentials. In like manner, IKVis smaller in hair cells and is activated at more depolarized potentials than in RPeD1.
Identification of the sex chromosome pair in coho salmon (Oncorhynchus kisutch): lack of conservation of the sex linkage group with chinook salmon (Oncorhynchus tshawytscha)
Authors: Phillips R.B. , Morasch M.R. , Park L.K. , Naish K.A. , Devlin R.H.
Published: August 2005

Fluorescence in situ hybridization (FISH) using a probe to the male-specific GH-Y (growth hormone pseudogene) was used to identify the Y chromosome in coho salmon (Oncorhynchus kisutch). The sex chromosome pair is morphologically similar to chinook salmon (Oncorhynchus tshawytscha) with the GH-Y localized to the small short arm of the largest subtelocentric chromosome pair. FISH experiments with probes containing sex-linked genes in rainbow trout (Oncorhynchus mykiss) (SCAR163) and chinook salmon (Omy7INRA) showed that the coho sex linkage group is different from chinook and rainbow trout and this was confirmed by segregation analysis for the Omy7INRA locus. The telomeric location of the SEX locus, the presence of shared male-specific markers in coho and chinook salmon, and the lack of conservation of sex-linkage groups suggest that transposition of a small male-specific region may have occurred repeatedly in salmonid fishes of the genus Oncorhynchus.
Variability of the 3′ApoB Minisatellite Locus in Eastern Slavonic Populations
Authors: Verbenko Dmitry A. , Knjazev A.N. , Mikulich A.I. , Khusnutdinova E.K. , Bebyakova N.A. , Limborska S.A.
Published: August 2005

Objective: To describe and compare the 3′ apolipoprotein (Apo) B minisatellite allele frequency distributions of Eastern Slavonic populations and their Uralic, Altaic, and Caucasian speaking neighbors. Methods: Healthy individuals of 10 populations among Russians, Byelorussians, Komis and Bashkirs were studied for variable number tandem repeats (VNTRs) in the 3′ApoB minisatellite region. Data were analyzed with other results reported for this polymorphism in eastern Europeans and Siberians. Results: Allele frequency spectra in Eastern Slavonic, Northern Caucasian and Finno-Ugric speaking populations are bimodal with the main peak in alleles 34–36 and a secondary mode around allele 48, whereas Altaic speaking populations have a unimodal allele frequency distribution with a peak of around 34–36 VNTRs. Population relationships were revealed using both multidimensional scaling analysis (based on Nei’s genetic distance estimate) and testing for genetic heterogeneity. Eastern Slavonic populations (Russians, Ukrainians, Byelorussians) were most closely related to each other and formed a separate tight clusterwhen plotted. Testing for genetic heterogeneity among the Eastern Slavonic ethnic groups revealed maximum diversity among Byelorussians, followed by Russians, then Ukrainians.The 3′ApoB minisatellite variability reveals little heterogeneityamong the Eastern Slavonic ethnic groups, whereas there wassignificant heterogeneity for Northern Caucasian and Altaic speakers. Conclusion: For this 3′ApoB polymorphism the Eastern Slavonic populations, despite their wide geographical distribution, appear to be much more homogenous than other ethnic groups of the region. Multidimensional scaling analysis of these data allowed for differentiation between individual populations from an ethnic group even if there is little heterogeneity.
Levetiracetam in the Treatment of Status epilepticus in Adults: A Study of 13 Episodes
Authors: Rossetti Andrea O. , Bromfield Edward B.
Published: August 2005

Treatment of status epilepticus (SE) has changed little over the last two decades, but the burden of this condition remains important. There is thus a need for alternative pharmacological therapies. Levetiracetam (LEV) has a wide spectrum of action and a favorable pharmacokinetic profile; however, little data exist regarding its use in SE. We identified patients with SE who received LEV, in a database comprising 127 SE episodes. Demographic, clinical and pharmacological data were analyzed, and compared to a control group consisting of 2 subjects from the database for each LEV patient, matched for age and sex. We identified 13 SE episodes occurring in 12 patients (10% of the database). Demographic, etiologic and clinical characteristics and outcome did not differ between the groups. Daily LEV dose ranged between 1,000–6,000 mg. Three patients were probable responders (23%), 1 responded to the treatment but subsequently died (8%), 4 were non-responders (31%, 1 died), and 5 had an undetermined response (38%). LEV may represent a useful alternative in the treatment of SE, particularly if a parenteral form of administration becomes available; to better define its role in this setting, prospective studies are needed.
Quality Control of Colorectal Surgery with an Extensive Complication Registration System
Authors: Vrancken Peeters Mark-Paul F.M. , Vrancken Peeters Marie-Jeanne T.F.D. , Corion Leonard U.M. , Breslau Paul J.
Published: August 2005

Background/Aims: Since 1996, a standard registration is used to obtain a clear understanding of the complications that occur after colorectal surgery. In our registration system the cause of a complication and the detrimental effect to the patient’s health are coded. Methods: The treatment of colorectal diseases was evaluated to analyze the quality of medical care. Results: From 1996 to 2000, a total of 169 complications were documented in 108 of the 353 patients operated on. Leakage of the anastomosis occurred in 22 cases (6%) and wound infection occurred in 11 cases (3%). Most of the complications required no or little medical attention (n = 101, 59%). 51% of the complications could be attributed to the physical condition of the patient. Surgical complications were the cause in 31% of the cases and management problems in 16% of the cases. Conclusion: A registration system provides good insight into the frequency and severity of the complications after colorectal surgery. Extensive registration is mandatory to provide reliable information, comparing the results year by year. This provides the basis for continuous improvement of medical protocols on the surgical ward.
Carboxypeptidase U (TAFIa): a metallocarboxypeptidase with a distinct role in haemostasis and a possible risk factor for thrombotic disease
Authors: Leurs Judith , Hendriks Dirk
Published: August 2005

Since the discovery of Carboxypeptidase U (CPU) in 1988, considerable information has been gathered about its biochemistry and function in physiological and pathophysiological circumstances. A variety of tools such as assays to measure proCPU and CPU, antibodies raised against (pro)CPU, selective CPU inhibitors and knock-out mice have been developed and are currently being used to explore the role of this metallocarboxypeptidase in different in vivo and in vitro settings. The knowledge that proCPU can be activated by thrombin and plasmin, enzymes with a key function in coagulation and fibrinolysis, and the ability of CPU to remove C-terminal lysine residues has led to the hypothesis that the proCPU/CPU pathway plays a role in the balance between coagulation and fibrinolysis. The maintenance of the equilibrium between coagulation and fibrinolysis is crucial for normal haemostasis and disturbance of this delicate balance can lead either to bleeding tendency or thrombosis. This review provides an update on several aspects of CPU known at the moment, including an extensive overview on the clinical studies performed up till now.

J. Leurs is a research assistant of the Fund for Scientific Research Flanders (FWO-Vlaanderen).
Do patients followed in anticoagulation clinics for antiphospholipid syndrome meet criteria for the disorder?
Authors: Kaboli Peter , Halfdanarson Thorvardur , Chan Happy , Hubert Rod , Rosen Seth , White Richard H. , Dunn Andrew S.
Published: August 2005

Although specific criteria for diagnosing the antiphospholipid syndrome (APS) exist (the Sapporo Criteria), most physicians are not aware these include repeat testing and documentation of either a lupus anticoagulant or medium to high levels of anticardiolipin antibody. Incorrect diagnosis of APS may result in unnecessary long-term anticoagulation. The purpose of this study was to determine the clinical and serological characteristics of patients being treated for APS and concordance with published criteria. This cross-sectional study identified APS patients who were being treated with warfarin at one of three universitybased anticoagulation clinics. Levels of anticardiolipin antibody were classified as low-positive if abnormal but <40 GPL/MPL units and medium/high-positive if ≥40 units. Strength of meeting Sapporo criteria was graded as definite, possible, and not meeting criteria. Of 103 cases, 97 had clinical and laboratory data available. Only 10 cases (10%, 95% Confidence Interval 5 - 19) met criteria for definite APS, 16 (16%, 10 - 26) had a possible diagnosis, and 71 (73%, 63 - 81) did not meet criteria. Of 70 cases that had abnormal anticardiolipin antibody results, only 32 (46%, 34 - 58) had medium/high-positive levels. Repeat laboratory testing was performed in only 49 cases (51%, 40 - 61). We conclude that few patients treated forAPS met Sapporo criteria. Abnormal levels of anticardiolipin antibody were frequently in the low-positive range, and repeat testing was often absent. A quality improvement program that includes review of cases referred for chronic anticoagulation care is recommended to ensure appropriate testing and treatment of patients with suspected APS.
ADAM15 is an adhesion receptor for platelet GPIIb-IIIa and induces platelet activation
Authors: Langer Harald , May Andreas E. , Bültmann Andreas , Gawaz Meinrad
Published: August 2005

Cell adhesion and proteolytic matrix degradation are central processes in atherosclerosis. Being a member of the family of ADAMs (“a disintegrin and metalloproteinase”), metargidin (ADAM15) combines a metalloproteinase domain and an RGD aminoacid sequence. We studied the potential role of ADAM15 as an adhesion receptor on endothelial cells and interactions between platelets and ADAM15 with respect to platelet adhesion, activation and thrombus formation. ADAM15 was found to be expressed on cultured endothelial cells (HUVEC). Platelet adhesion to immobilized recombinantADAM15 was effectively enhanced under both static and high shear rate conditions reaching the maximum level of adhesion to fibrinogen. Consistently, platelet adhesion onto ADAM15 overexpressing endothelial cells was significantly increased. Adhesion to ADAM15 was reduced by blockade of GPIIb-IIIa using neutralizing anti-αIIbβ3 mAbs (7E3, 2G12), but not by anti-α
v
β3 (LM609). Soluble ADAM15 binds to activated but not to resting GPIIb-IIIa. Moreover, platelets adherent to ADAM15 additionally attracted platelets under high shear rates indicating an initial role of platelet- ADAM15 interactions for thrombus formation. Furthermore, incubation of platelets with solubleADAM15 showed a dose-dependent increase in secretion of CD62P and CD40L. ADAM15 is expressed on endothelial cells and can serve as an adhesion receptor for platelets via GPIIb-IIIa binding. Platelet adhesion to ADAM15 leads to platelet activation, secretion and promotes thrombus formation. Thus, ADAM15 may represent a novel target for antithrombotic strategies in cardiovascular pathologies.
Postprandial elevation of tissue factor antigen in the blood of healthy adults
Authors: Mackman Nigel , Tilley Rachel E. , Rutledge John C. , Motton Deborah D.
Published: August 2005

Atherosclerosis is a dynamic disease involving lipid metabolism, inflammation and thrombosis. A key factor in thrombosis is tissue factor, a small transmembrane glycoprotein. Tissue factor binds FactorVIIa, and this complex converts Factor X to Factor Xa, leading to thrombin generation and fibrin formation. Inhibition of this pathway is by tissue factor pathway inhibitor (TFPI). Tissue factor is found sequestered within atherosclerotic plaques, and plaque rupture allows tissue factor exposure to the circulation, leading to formation of a thrombus. Tissue factor is also associated with membrane microparticles in the circulation, most likely released from monocytes activated by an inflammatory event. We hypothesize that consumption of a typical western diet that is moderate in fat content leads to elevated levels of circulating tissue factor that may act as a marker of a pro-thrombotic state. Healthy volunteers, aged 18-55, consumed a moderate (40%) fat meal, with blood taken before and 3.5 and 6 h after the meal. Plasma was isolated and assayed for plasma triglycerides, tissue factor, thrombin antithrombin (TAT) complexes, TFPI and TNFα. The levels of circulating tissue factor increased 56% (from 78 pg/ml to120 pg/ml) 3.5 h after the meal. Levels decreased, but had not returned to baseline 6 h postprandially. No significant differences in TAT, TFPI and TNFá levels were observed postprandially. These results demonstrate increased tissue factor levels in individuals who consumed a moderate fat diet. This suggests that the typical western diet may play a larger role in cardiovascular disease than merely altering lipid profiles.
The decellularized porcine heart valve matrix in tissue engineering
Authors: Kasimir Marie-Theres , Weigel Guenter , Sharma Jyotindra , Rieder Erwin , Seebacher Gernot , Wolner Ernst , Simon Paul
Published: August 2005

An approach in tissue engineering of heart valves is the use of decellularized xenogeneic matrices to avoid immune response after implantation. The decellularization process must preserve the structural components of the extracellular matrix to provide a biomechanically stable scaffold. However, it is known that in vascular lesions platelet adhesion to extracellular matrix components occurs and platelet activation is induced. In the present study we examined the effects of a decellularized porcine heart valve matrix on thrombocyte activation and the influence of re-endothelialisation in vitro. Porcine pulmonary conduits were decellularized using Triton X-100, Na-deoxycholate and Igepal CA-630® followed by a ribonuclease digestion. Cryostat sections of decellularized heart valves with and without seeding with human umbilical vein endothelial cells (HUVEC) were incubated with platelet rich plasma. Samples were either stained with fluorescent antibodies for CD41 and PAC-1 (recognizing the activated fibrinogen receptor) or fixed with glutaraldehyde. Thereafter, the samples were processed for laser scanning microscopy (LSM) or scanning electron microscopy (SEM). Examination by LSM showed numerous platelets with co-localized staining for CD41 and PAC-1 on the nonseeded decellularized heart valve matrix whereas after seeding with endothelial cells no platelet activation was detected. SEM revealed platelet adhesion and aggregate formation only on the surface of the non-seeded or partially denuded matrix specimens. We show in this study that the decellularized porcine matrix acts as a platelet-activating surface. Seeding with endothelial cells effectively abolishes the platelet adhesion and activation and therefore is necessary to eliminate thrombogenicity in tissue engineered heart valves.
Effect of nitroxyl on human platelets function
Authors: Bermejo Emilse , Alberto Fabiana , Rosenstein Ruth E. , Bari Sara E. , Lazzari María A. , Sáenz Daniel A.
Published: August 2005

There is a growing body of evidence on the role of nitric oxide (NO) in human platelet physiology regulation. Recently, interest has developed in the functional role of an alternative redox form of NO, namely nitroxyl (HNO/NO-), because it is formed by a number of diverse biochemical reactions. The aim of the present study was to comparatively analyze the effect of HNO and NO on several functional parameters of human platelets. For this purpose, sodium trioxodinitrate (Angeli’s salt, AS) and sodium nitroprusside (SNP) were used as HNO and NO releasers, respectively. Both AS and SNP significantly inhibited platelet aggregation and ATP release induced by different agonists and adrenaline. AS or SNP did not modify the expression of platelet glycoproteins (Ib, IIb-IIIa, Ia-IIa, IV), whereas they substantially decreased the levels of CD62P, CD63 and of PAC-1 (a platelet activated glycoprotein IIb/IIIa epitope) after the stimulation with ADP. AS and SNP significantly increased cGMP accumulation in a 1H-[1,2,4]oxadiazolo [4,3-a] quinoxalin-1-one (ODQ)-sensitive manner. However, while L-cysteine reduced the effect of AS, it increased the effect of SNP on this parameter. Accordingly, a differential effect of L-cysteine was observed on the antiaggregatory effect of both compounds. In summary, these results indicate that HNO is an effective inhibitor of human platelet aggregation.
Drug interactions and risk of acute bleeding leading to hospitalisation or death in patients with chronic atrial fibrillation treated with warfarin
Authors: Hollowell Jennifer , Meier Christoph R. , Haefeli Walter E. , Gasse Christiane
Published: August 2005

Although drug interactions with warfarin are an important cause of excessive anticoagulation, their impact on the risk of serious bleeding is unknown. We therefore performed a cohort study and a nested case-control analysis to determine the risk of serious bleeding in 4152 patients (aged 40–84 years) with nonvalvular atrial fibrillation (AF) taking long-term warfarin (>3 months). The study population was drawn from the UK General Practice Research Database. More than half (58%) of eligible patients used potentially interacting drugs during continuous warfarin treatment. Among 45 identified cases of incident idiopathic bleeds (resulting in hospitalisation within 30 days or death within 7 days) and 143 matched controls, more cases than controls took ≥1 potentially interacting drug within the preceding 30 days (62.2% vs. 35.7%) and used >4 drugs (polypharmacy) within the preceding 90 days (80.0% vs. 66.4%). Conditional logistic regression analysis yielded an odds ratio (OR) of 3.4 (95% confidence interval [CI]: 1.4–8.5) for the risk of serious bleeding in patients treated with warfarin and ≥1 drugs potentially increasing the effect of warfarin vs. warfarin alone adjusted for polypharmacy, diabetes, hypertension, heart failure, and thyroid disease; the adjusted OR for the combined use of warfarin and aspirin vs. warfarin alone was 4.5 (95% CI: 1.1–18.1). We conclude that concurrent use of potentially interacting drugs with warfarin is associated with a 3 to 4.5-fold increased risk of serious bleeding in long-term warfarin users.
The potential role of platelet microparticles in atherosclerosis
Authors: Tan Kiat T. , Lip Gregory Y. H.
Published: August 2005

The release of microvesicles (‘platelet microparticles’, PMPs) by activated platelets has been shown to be an integral part of the thrombotic process. PMPs are believed to mediate many biological processes as they possess various platelet membrane proteins and bioactive lipids. Of note, there is a growing body of evidence that PMPs are involved in all stages in the pathobiology of atherosclerosis. In addition to their role in thrombosis, PMPs may also have a pro-inflammatory effect, which promotes the development of atherosclerosis. Also, bioactive lipids in PMPs have been shown to have important effects on angiogenesis. This review summarises the various studies on the possible role of PMPs in the progression of atherosclerosis.
Stereoselective inhibition of human platelet aggregation by R-138727, the active metabolite of CS-747 (Prasugrel, LY640315), a novel P2Y12 receptor inhibitor
Authors: Hasegawa Michihiro , Sugidachi Atsuhiro , Ogawa Taketoshi , Isobe Takashi , Jakubowski Joseph A. , Asai Fumitoshi
Published: August 2005

CS-747 (Prasugrel, LY640315) is a thienopyridine antiplatelet prodrug that is metabolized to the thiol-containing active metabolite R-138727, which binds to and irreversibly inhibits the platelet P2Y12 ADP receptor. R-138727 is composed of 4 stereoisomers, (R, S)-, (R, R)-, (S, S)-, and (S, R)-isomers (the first letter for the configuration of a chiral center at the sulfur-bearing position and the second for that at the benzylic position). In the present study, we determined the stereoselectivity of P2Y12 antagonist effects by assessing the antagonism of the [3H]-2-MeS-ADP that binds to human P2Y12 receptors expressed in Chinese hamster ovary cells as an affinity assay, and by the inhibition of ADP-induced aggregation of washed human platelets as a functional assay. R-138727 and its 2 components, R-99224, a mixture of (R, S)- and (S, R)-isomers and R-100364, a mixture of (R, R)- and (S, S)-isomers, inhibited [3H]-2-MeS-ADP binding and platelet aggregation. The rank order of potency of these compounds were identical in both assays: R-99224>R-138727>> R-100364. Inhibition of ADP-induced platelet aggregation by R-138727 and R-99224 was concentration- and time-related. In experiments using the 4 single stereo-isomers, all isomers inhibited ADP-induced platelet aggregation, but the (R, S)-isomer was found to be the most potent, followed by the (R, R)-isomer. These in vitro studies indicate that R-138727 is an effective antagonist of P2Y12 and potent inhibitor of ADP-induced platelet aggregation, and that these antiplatelet activities of R-138727 are largely dependent on its (R, S)-isomer. This suggests that the (R)- configuration of the reactive thiol group of the active metabolite of CS-747 is critical for P2Y12 and platelet inhibitory activities.
Association of MTRR A66G polymorphism (but not of MTHFR C677T and A1298C, MTR A2756G, TCN C776G) with homocysteine and coronary artery disease in the French population
Authors: Juilliére Yves , Candito Mirande , Adjalla Charles E. , Gibelin Pierre , Herbeth Bernard , Obberghen Emmanuel Van , Guéant Jean-Louis , Guéant-Rodriguez Rosa-Maria
Published: August 2005

methylenetetrahydrofolate reductase polymorphism (MTHFR C677T) is an established determinant of homocysteine plasma level (t-Hcys) while its association with coronary artery disease (CAD) seems to be more limited. In contrast, the association of the substitutions A2756G of methionine synthase (MTR), A66G of methionine synthase reductase (MTRR) and C776G of transcobalamin (TCN) to both t-Hcys and CAD needs to be evaluated further. The objective was to evaluate the association of these polymorphisms with t-Hcys and CAD in a French population. We investigated the individual and combined effects of these polymorphisms and of vitamin B12 and folates with t-Hcys in 530 CAD patients and 248 matched healthy controls. t-Hcys was higher in the CAD group than in controls (11.8 vs 10.4 μM, P<0.0001) and in carriers of MTRR AA and MTHFR 677TT than in those carrying the most frequent allele of both polymorphisms (13.8 vs 11.4 μM, P=0.0102 and 12.5 vs 11.0 mM, P=0.0065 respectively). The frequency of MTRR A allele was higher in CAD patients than in controls (0.48 [95% CI: 0.44-0.52] vs 0.38 [95% CI: 0.32-0.44], P=0.0081) while no difference was observed for MTHFR 677T frequency. In multivariate analysis, t-Hcys > median and MTRR AA genotype were two significant independent predictors of CAD with respective odds ratios of 3.1 (95 % CI: 1.8-5.1, P<0.0001) and 4.5 (95% CI: 1.5-13.1, P=0.0051). In conclusion, in contrast to North Europe studies, MTRR AA genotype is a genetic determinant of moderate hyperhomocysteinemia associated with CAD in a French population without vitamin fortification.
Internal Atmospheric Dynamics and Tropical Indo-Pacific Climate Variability
Authors: Kirtman Ben P. , Pegion Kathy , Kinter Saul M.
Published: August 2005

One possible explanation for tropical sea surface temperature (SST) interannual variability is that it can be accurately described by a linear autoregressive model with damped coupled feedbacks and stochastic forcing. This autoregressive model can be viewed as a “null hypothesis” for tropical SST variability. This paper advances a new coupled general circulation model (CGCM) coupling strategy, called an interactive ensemble, as a method to test this null hypothesis. The design of the interactive ensemble procedure is to reduce the stochastic variability in the air–sea fluxes applied to the ocean component while retaining the deterministic component of the coupled feedbacks. The interactive ensemble procedure uses multiple realizations of the atmospheric GCM coupled to a single realization of the ocean GCM. The ensemble mean of the atmospheric GCM fluxes are applied to the ocean model thereby significantly reducing the variability due to internal atmospheric dynamics in the air–sea fluxes. If the null hypothesis is correct, the SST variability is reduced, and the autoregressive model defines how much the variability should be reduced. To test the null hypothesis, the interactive ensemble procedure is applied to a heuristic coupled model. Then the heuristic coupled model is used to interpret the CGCM interactive ensemble results with respect to (i) SST variance and (ii) how the amplitude of atmospheric internal dynamics depends on the evolving background SST anomaly. There are significant regions where the heuristic model fails to reproduce the CGCM results, suggesting that aspects of tropical Indo-Pacific variability in the CGCM cannot be explained by damped coupled feedbacks and stochastic forcing. These regions are largely coincident with regions of large convective anomalies. Surprisingly, significant regions were found in the tropical eastern Pacific where the variability due to internal ocean dynamics cannot be neglected.
Freezing Drizzle Formation in Stably Stratified Layer Clouds. Part II: The Role of Giant Nuclei and Aerosol Particle Size Distribution and Solubility
Authors: Geresdi István , Rasmussen Roy
Published: August 2005

This paper investigates how the characteristics of aerosol particles (size distribution and solubility) as well as the presence of giant nuclei affect drizzle formation in stably stratified layer clouds. A new technique was developed to simulate the evolution of water drops from wet aerosol particles and implemented into a detailed microphysical model. The detailed microphysical model was incorporated into a one-dimensional parcel model and a two-dimensional version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5). Sensitivity experiments were performed with the parcel model using a constant updraft speed and with the two-dimensional model by simulating flow over a bell-shaped mountain. The results showed that 1) stably stratified clouds with weak updrafts (<10 cm s−1) can form drizzle relatively rapidly for maritime size distributions with any aerosol particle solubility, and for continental size distributions with highly insoluble particles due to the low number of activated cloud condensation nuclei (CCN) (<100 cm−3), 2) drizzle is suppressed in stably stratified clouds with weak updrafts (<10 cm s−1) for highly soluble urban and extreme urban size distributions, and 3) the presence of giant nuclei only has an effect on drizzle formation for the highly soluble continental aerosol size distributions.
Simulations of the Atmospheric General Circulation Using a Cloud-Resolving Model as a Superparameterization of Physical Processes
Authors: Khairoutdinov Marat , Randall David , DeMott Charlotte
Published: August 2005

Traditionally, the effects of clouds in GCMs have been represented by semiempirical parameterizations. Recently, a cloud-resolving model (CRM) was embedded into each grid column of a realistic GCM, the NCAR Community Atmosphere Model (CAM), to serve as a superparameterization (SP) of clouds. Results of the standard CAM and the SP-CAM are contrasted, both using T42 resolution (2.8° × 2.8° grid), 26 vertical levels, and up to a 500-day-long simulation. The SP was based on a two-dimensional (2D) CRM with 64 grid columns and 24 levels collocated with the 24 lowest levels of CAM. In terms of the mean state, the SP-CAM produces quite reasonable geographical distributions of precipitation, precipitable water, top-of-the-atmosphere radiative fluxes, cloud radiative forcing, and high-cloud fraction for both December–January–February and June–July–August. The most notable and persistent precipitation bias in the western Pacific, during the Northern Hemisphere summer of all the SP-CAM runs with 2D SP, seems to go away through the use of a small-domain three-dimensional (3D) SP with the same number of grid columns as the 2D SP, but arranged in an 8 × 8 square with identical horizontal resolution of 4 km. Two runs with the 3D SP have been carried out, with and without explicit large-scale momentum transport by convection. Interestingly, the double ITCZ feature seems to go away in the run that includes momentum transport.

The SP improves the diurnal variability of nondrizzle precipitation frequency over the standard model by precipitating most frequently during late afternoon hours over the land, as observed, while the standard model maximizes its precipitation frequency around local solar noon. Over the ocean, both models precipitate most frequently in the early morning hours as observed. The SP model also reproduces the observed global distribution of the percentage of days with nondrizzle precipitation rather well. In contrast, the standard model tends to precipitate more frequently, on average by about 20%–30%. The SP model seems to improve the convective intraseasonal variability over the standard model. Preliminary results suggest that the SP produces more realistic variability of such fields as 200-mb wind and OLR, relative to the control, including the often poorly simulated Madden–Julian oscillation (MJO).
A Refinement of the Millionshchikov Quasi-Normality Hypothesis for Convective Boundary Layer Turbulence
Authors: Gryanik Vladimir M. , Hartmann Jörg , Raasch Siegfried , Schröter Michael
Published: August 2005

The Millionshchikov hypothesis of quasi-normal distribution of fourth-order moments fails for convective conditions where the probability density functions of temperature and vertical velocity fluctuations are skewed. This is shown for aircraft and large-eddy simulation (LES) data, and new closures for fourth-order moments that take the skewness into account are suggested. These new closures are in very good agreement with the data.
Drag-Induced Transfer of Horizontal Momentum between Air and Raindrops
Authors: Shapiro Alan
Published: August 2005

A theoretical model for unsteady drag-induced transfer of horizontal momentum between air and raindrops in moderate to heavy rainfall is presented. The model accounts for a two-way coupling in which the relative horizontal motion between air and raindrops appears as a drag forcing in both the air and raindrop equations of motion. Analytical solutions of these coupled equations are obtained for the case of rain falling through (i) an initial step change in environmental wind, (ii) a uniform shear profile, and (iii) periodically varying vertical shears of various wavenumbers (a crude proxy for turbulent eddies). Formulas for the propagation (descent) speeds of the shear zones are obtained for (ii), (iii), and for the later stage of (i). However, these speeds are generally quite small—on the order of a few centimeters per second even for heavy rainfall. More importantly, the solutions of (i) and (iii) indicate that the drag interaction leads to a decay of the velocity gradients. A formula for the e-folding decay time of the periodically varying shear profiles indicates that at small wavelengths, the smallest decay times are found for the smaller drops, but at large wavelengths, the smallest decay times are found for the larger drops. The decay times decrease with decreasing wavelength, and approach a value equal to the reciprocal of the product of the rainwater mixing ratio and a drag parameter in the limit of vanishing wavelength. For parameters typical of moderate to heavy rainfall, the small-scale decay times are on the order of a few minutes.
A New Scaling for Tornado-Like Vortices
Authors: Nolan David S.
Published: August 2005

A new approach is presented for the nondimensionalization of the Navier–Stokes equations for tornado-like vortices. This scaling is based on the results of recent numerical simulations and physical reasoning. The method clarifies and unifies the results of numerous earlier studies that used numerical simulations of axisymmetric incompressible flow to study tornadoes. Some examples are presented.