Biomedical subjects

R Graf

Publications and source records attributed to R Graf.

At least 19 recordsLinked to original sources

PubMed2001

Proatherogenic flow conditions initiate endothelial apoptosis via thrombospondin-1 and the integrin-associated protein.

Recently it has been shown that vascular endothelial cells (EC) are completely devoid of apoptosis if cultivated under a steady laminar flow and that apoptosis is induced by turning off the flow. An autocrine loop of thrombospondin-1 (TSP-1) and the alpha(v)beta(3) integrin/integrin-associated protein (IAP) complex has been identified as the molecular coupling device between flow and apoptosis. Lack of blood flow is a rare and mostly transient phenomenon whereas irregular flow conditions are permanently present at arterial bifurcations and sites of abnormal vessel morphology. Irregular flow conditions are established here either by the action of a cone-and-plate type flow apparatus generating a uniform turbulent flow or in a flow chamber by insertion of a local hindrance creating a zone of unsteady laminar flow with vortex formation and lowered shear stress. In both cases apoptosis is induced either throughout the entire monolayer or restricted to the locally defined area. Flow disturbance and apoptosis are coupled by the described autocrine loop of TSP-1 and the integrin/IAP receptor complex. In vivo atherosclerotic lesions occur predominantly at sites of flow irregularities, which are thought to be pro-atherogenic. Thus we propose a key role of the identified mechanosensitive apoptosis induction for the initiation of atherosclerosis.

Antigens, CD↗

PubMed2001

A family of 16-kDa pancreatic secretory stress proteins form highly organized fibrillar structures upon tryptic activation.

A group of 16-kDa proteins, synthesized and secreted by rat pancreatic acinar cells and composed of pancreatic stone protein (PSP/reg) and isoforms of pancreatitis-associated protein (PAP), show structural homologies, including conserved amino acid sequences, cysteine residues, and highly sensitive N-terminal trypsin cleavage sites, as well as conserved functional responses in conditions of pancreatic stress. Trypsin activation of recombinant stress proteins or counterparts contained in rat pancreatic juice (PSP/reg, PAP I and PAP III) resulted in conversion of 16-kDa soluble proteins into 14-kDa soluble isoforms (pancreatic thread protein and pancreatitis-associated thread protein, respectively) that rapidly polymerize into insoluble sedimenting structures. Activated thread proteins show long lived resistance to a wide spectrum of proteases contained in pancreatic juice, including serine proteases and metalloproteinases. In contrast, PAP II, following activation with trypsin or pancreatic juice, does not form insoluble structures and is rapidly digested by pancreatic proteases. Scanning and transmission electron microscopy indicate that activated thread proteins polymerize into highly organized fibrillar structures with helical configurations. Through bundling, branching, and extension processes, these fibrillar structures form dense matrices that span large topological surfaces. These findings suggest that PSP/reg and PAP I and III isoforms consist of a family of highly regulated soluble secretory stress proteins, which, upon trypsin activation, convert into a family of insoluble helical thread proteins. Dense extracellular matrices, composed of helical thread proteins organized into higher ordered matrix structures, may serve physiological functions within luminal compartments in the exocrine pancreas.

Amino Acid Sequence↗

PubMed2001

Charge-coupled device camera-based detection of fluorescence-labeled proteins immobilized on nitrocellulose membranes.

Proteins dotted on nitrocellulose membranes are biotinylated by reaction with a biotinyl-succinimide ester. The resulting biotinyl residues serve as specific binding sites for a subsequent streptavidin-based detection system. Using streptavidin-peroxidase, the proteins are visualized either by deposition of a colored formazan dye or by enhanced chemiluminescence the latter being twofold more sensitive. Alternatively, streptavidin-fluorescein isothiocyanate (FITC) is substituted for the peroxidase conjugate as tool for protein staining. The sensitivity of both staining variants is dramatically improved by the inclusion of the reporter deposition technique. The fluorescence-labeled proteins are visualized on a visible blue light emitting illuminator preventing the bothering effect of photobleaching. In combination with a charge-coupled device (CCD) camera-based image analyzing system the established stain with streptavidin-FITC detects about 10 pg of protein dot blotted on nitrocellulose membranes.

Biotinylation↗

PubMed2001

Recoupled polarization-transfer methods for solid-state (1)H--(13)C heteronuclear correlation in the limit of fast MAS.

An in-depth account of the effects of homonuclear couplings and multiple heteronuclear couplings is given for a recently published technique for (1)H--(13)C dipolar correlation in solids under very fast MAS, where the heteronuclear dipolar coupling is recoupled by means of REDOR pi-pulse trains. The method bears similarities to well-known solution-state NMR techniques, which form the framework of a heteronuclear multiple-quantum experiment. The so-called recoupled polarization-transfer (REPT) technique is versatile in that rotor-synchronized (1)H--(13)C shift correlation spectra can be recorded. In addition, weak heteronuclear dipolar coupling constants can be extracted by means of spinning sideband analysis in the indirect dimension of the experiment. These sidebands are generated by rotor encoding of the reconversion Hamiltonian. We present generalized variants of the initially described heteronuclear multiple-quantum correlation (HMQC) experiment, which are better suited for certain applications. Using these techniques, measurements on model compounds with (13)C in natural abundance, as well as simulations, confirm the very weak effect of (1)H--(1)H homonuclear couplings on the spectra recorded with spinning frequencies of 25--30 kHz. The effect of remote heteronuclear couplings on the spinning-sideband patterns of CH(n) groups is discussed, and (13)C spectral editing of rigid organic solids is shown to be practicable with these techniques.

Journal Article↗

PubMed2001

Screening spring wheat for midge resistance in relation to ferulic acid content.

The concentration of ferulic acid (FA), the major phenolic acid in the wheat kernel, was found to differ significantly in the mature grain of six wheat cultivars known to have a range of tolerance to the orange wheat blossom midge (Sitodiplosis mosellana). Differences in FA content were correlated with floret infestation level of the cultivars. The wheat cultivars ranked similarly in FA content at the four locations where they were tested, despite a significant effect of environment. Ferulic acid was synthesized mainly during the early stages of grain filling but at different rates among cultivars. Ferulic acid was concentrated primarily in the shorts and bran fractions in an insoluble-bound form. A high correlation was obtained between FA contents as determined by GLC, fluorometry, UV, and colorimetry. The colorimetric procedure was modified as a qualitative, simple, and rapid test for identifying midge-resistant wheat and evaluated in several field trials. The method should provide a rapid tool in the preliminary screening of experimental lines in the development of midge-resistant wheat cultivars.

Animals↗

PubMed2001

Vascular endothelial cells express a functional fas-receptor due to lack of hemodynamic forces.

The fas system is present in atherosclerotic lesions. However, its role in the initiation and progression is still unclear. Here we show that in endothelial cells (EC) the expression of the fas receptor is regulated by flow conditions. The EC of the vascular system are regularly exposed to a range of hemodynamic forces with great impact on cellular structures and functions. Recently it was reported that in endothelial cells the lack of hemodynamic forces as well as irregular flow conditions trigger apoptosis by induction of a mechanosensitive autocrine loop of thrombospondin-1 and the alpha(V)beta(3) integrin/integrin-associated protein complex. Here we show that EC cultivated under regular laminar flow conditions are devoid of the fas-receptor whereas cultivation under static conditions as well as under turbulence leads to its expression. Stimulation of the fas-receptor by its ligand increases the amount of apoptotic cells by twofold; the increase can be prevented by blocking the fas-receptor. The availability of the expressed fas receptor for stimulation by its ligand hints at a role as a tool for progression of atherosclerosis.

Apoptosis↗

PubMed2001

[Technical errors in the application of Graf's hip sonography method].

AIM: The aim of the study is to point out possible examination errors because of a titled transducer, and to analyse their sources. METHODS: The results obtained by experienced examiners using the correct examination technique were compared to results obtained under defined deviations from the standard. With the use of a computer model the course taken by the ultrasound waves in the neonatal hip was simulated and the sonographic image reconstructed. RESULTS: Twisted as well as tilted positions of the transducer lead to significant errors in alpha, the acetabular roof angle. This is in accordance with the computer model predictions. Caudo-cranially tilted probes lead to false-positive, therapeutically relevant incorrect diagnoses. CONCLUSION: The computer simulation predicts a high degree of accuracy of hip sonography in Graf's technique under standard conditions. The effectiveness of sonographic infant hip screening largely depends on the ability to adhere to the standardized approach, minimizing possible errors. A mechanical transducer guide prevents tilting errors by reducing the degrees of variability in positioning the transducer.

Artifacts↗

PubMed2001

Adenosine in relation to calcium homeostasis: comparison between gray and white matter ischemia.

In vitro studies suggest that adenosine may attenuate anoxic white matter damage as an intrinsic protective substance. The authors investigated ischemic alterations of purines in relation to tissue depolarization and extracellular calcium and amino acid concentrations in vivo using microdialysis and ion-selective electrodes in cortical gray and subcortical white matter of 10 cats during 120 minutes of global brain ischemia. Immediately on induction of ischemia, regional cerebral blood flow ceased in all cats in both gray and white matter. The direct current potential rapidly decreased, the decline being slower and shallower in white matter. Extracellular calcium levels decreased in gray matter. In contrast, they first increased in white matter and started to decrease below control levels only after approximately 30 minutes. Adenosine levels transiently increased in both tissue compartments; the peak was delayed by 30 minutes in white matter. Thereafter, levels declined faster in gray than in white matter and remained elevated in the latter tissue compartment. Inosine and hypoxanthine elevations were progressive in both regions but smaller in white matter. Levels of gamma-aminobutyric acid, another putatively protective agent, steadily increased, starting immediately in gray matter and delayed by almost 1 hour in white matter. The delayed and prolonged accumulation of adenosine correlates with a slower adenosine triphosphate breakdown in white matter ischemia and may result in protection of white matter by suspending cellular calcium influx.

Adenosine↗

PubMed2001

Histopathologic and morphometric evaluation of the skin abnormalities induced by erbium:YAG and carbon dioxide lasers in 10 patients.

In the 1960s, carbon dioxide (CO2) laser therapy started to be applied to eliminate wrinkles, actinic scars, and acne because of its capacity of induce intracellular water vaporization. However, recent studies have shown the efficacy of the erbium laser in removing delicate and moderate scars. Furthermore, the postoperative lesions induced by the erbium laser seem to resolve faster and with less erythematous pattern compared with lesions induced by the CO2 laser. The purpose of this study was to determine the immediate pathologic alterations caused by single applications of CO2 and erbium lasers and their association in human skin shreds. Ten white female patients aged 30 to 63 years underwent rhytidectomy, and their respective shreds, which were prepared for excision, were tattooed with the CO2 laser, the erbium laser, or a combination of both in random order and number of applications, before final removal. This project was approved by the local ethical committee. After surgical removal, these tattooed shreds were fixed in 10% buffered formalin and submitted to histopathologic analysis. Morphometric studies demonstrated the normal skin thickness and thickness of the laser-treated area, and their subtraction resulted in the ablation damage values. Residual thermal damage corresponded to the thickness of the affected skin from the most superficial layer of tissue in the laser-treated area down to the deepest dermal area with basophilic degeneration of collagen fibers. Our results showed that two CO2 applications resulted in greater ablation and residual thermal damage when compared with only one CO2 application. The same was true in comparisons of one and two applications of the erbium laser. Both results were statistically significant (p < 0.05). When one isolated erbium and one isolated CO2 application were compared, ablation damage was greater in the former group, although with no statistical significance. One CO2 plus one erbium application compared with one isolated CO2 application showed similar ablation damage but greater residual thermal damage in the latter group (p < 0.05). These observations might contribute to our understanding of the lesions caused in the human skin by erbium and CO2 lasers and eventually help determine the ideal laser combination for the appropriate surgical treatment.

Adult↗

PubMed2001

Conformational changes of pancreatitis-associated protein (PAP) activated by trypsin lead to insoluble protein aggregates.

Pancreatitis-associated protein (PAP), a secretory acute-phase protein of the pancreatic acinar cell, is highly up-regulated early in acute pancreatitis. PAP expression returns to undetectable levels when the pancreas recovers. In the rat, three isoforms of PAP are known, all of which are upregulated during acute pancreatitis. Their functions remain obscure. Pancreatic stone protein (PSP/reg), which shows strong sequence homology to PAP, is secreted into pancreatic juice under physiologic and pathologic conditions. PSP/reg is highly susceptible to trypsin cleavage at its ARG11-ILE12 bond. Cleavage results in an N-terminal undecapeptide and a C-terminal peptide called pancreatic thread protein (PTP). PTP forms oligomeric fibrillar structures, which spontaneously sediment in vitro. PTP can be found in protein plugs or stones from patients with chronic pancreatitis. Rat PAP contains a trypsin cleavage site at the same position as PSP/reg. We hypothesize that PAP is susceptible to tryptic cleavage, and that the C-terminal cleavage product of PAP spontaneously precipitates at neutral pH. To test our hypothesis, we generated and purified recombinant PAP. Here we report the production of rat PAP I, II, and III in a yeast expression system using Pichia pastoris. We demonstrate in vitro the tryptic cleavage of rat PAP and the formation of a spontaneously precipitating peptide, which we call pancreatitis-associated thread protein (PATP). PATP displays pH-dependent solubility characteristics very similar to those of PTP.

Acute-Phase Proteins↗

PubMed2001

Random circular permutation leading to chain disruption within and near alpha helices in the catalytic chains of aspartate transcarbamoylase: effects on assembly, stability, and function.

A collection of circularly permuted catalytic chains of aspartate transcarbamoylase (ATCase) has been generated by random circular permutation of the pyrB gene. From the library of ATCases containing permuted polypeptide chains, we have chosen for further investigation nine ATCase variants whose catalytic chains have termini located within or close to an alpha helix. All of the variants fold and assemble into dodecameric holoenzymes with similar sedimentation coefficients and slightly reduced thermal stabilities. Those variants disrupted within three different helical regions in the wild-type structure show no detectable enzyme activity and no apparent binding of the bisubstrate analog N:-phosphonacetyl-L-aspartate. In contrast, two variants whose termini are just within or adjacent to other alpha helices are catalytically active and allosteric. As expected, helical disruptions are more destabilizing than loop disruptions. Nonetheless, some catalytic chains lacking continuity within helical regions can assemble into stable holoenzymes comprising six catalytic and six regulatory chains. For seven of the variants, continuity within the helices in the catalytic chains is important for enzyme activity but not necessary for proper folding, assembly, and stability of the holoenzyme.

Amino Acid Sequence↗

PubMed2001

Relevance of experimental ischemia in cats for stroke management: a comparative reevaluation.

Repeat studies in animal models of acute focal ischemia can be compared to incidental studies in the course of ischemic stroke in order to shed light on the development of changes causing ischemic infarcts or recovery of critically perfused tissue. Positron emission tomography (PET) studies of regional cerebral blood flow, cerebral metabolic rate for oxygen, oxygen extraction fraction (OEF), cerebral metabolic rate of glucose and flumazenil (FMZ) binding in the cat middle cerebral artery occlusion (MCAO) model and in patients with acute ischemic hemispheric stroke were reviewed. After permanent MCAO, the development of "misery-perfused" penumbral tissue and its centrifugal conversion into necrosis could be demonstrated, resembling focal pathophysiological changes in patients with ischemic attacks. In the experimental model and in vascular insults in humans, a chance of recovery existed if collateral perfusion developed spontaneously within the first hours. In transient MCAO, reperfusion was only effective in preventing infarction when it was initiated as long as misery perfusion persisted; in these cases tissue was salvaged and large infarcts did not develop. In the other instances when oxygen metabolism broke down, and an increased OEF was no longer seen, reperfusion even at levels above preocclusion had no effect, and large space-occupying infarcts developed. These experimental findings are comparable to the variable outcome after thrombolytic therapy; if reperfusion is achieved within the therapeutic window of tissue viability, large infarcts are prevented and complete or partial recovery can be achieved. In the experimental model of focal ischemia and in human stroke, FMZ can be utilized as a marker of neuronal integrity. If FMZ binding in the cortex is decreased below 4 times the mean value of white matter in the acute stage, permanent infarcts were observed on late CT/MRI; this irreversible damage could not be prevented by thrombolytic therapy. These results demonstrated that PET studies in suitable ischemia models in cats can help to explain various courses and diverging outcomes of acute ischemic stroke. Comparable findings from experimental ischemia and human stroke may affect the selection of appropriate therapeutic strategies.

Animals↗

PubMed2001

Calcium ion transients in peri-infarct depolarizations may deteriorate ion homeostasis and expand infarction in focal cerebral ischemia in cats.

BACKGROUND AND PURPOSE: Harmful effects of peri-infarct depolarizations (PIDs) may depend on recurrent Ca(2+) influx. Thus far, few studies have documented the relevance of PIDs in gyrencephalic animals, and the progressive nature of this process has not been investigated over extended periods. We therefore studied in prolonged focal ischemia in cats spatial and temporal profiles of extracellular calcium ([Ca(2+)](o)) shifts in relation to direct current (DC) potential, nitric oxide (NO) concentration and regional cerebral blood flow alterations, and final pathological outcome. METHODS: In halothane-anesthetized cats receiving either vehicle (n=12) or MK-801 treatment (5 mg/kg IV; n=10), the left middle cerebral artery was permanently occluded. Laser-Doppler probes, ion-selective microelectrodes, and NO electrodes measured simultaneously regional cerebral blood flow, DC potential, electrocorticogram, [Ca(2+)](o), and NO concentrations in ectosylvian and suprasylvian gyri of the left cerebral cortex. RESULTS: Persistent depolarization immediately after middle cerebral artery occlusion occurred in 10 ectosylvian and 4 suprasylvian gyri of vehicle-treated animals and in 9 ectosylvian and 3 suprasylvian gyri of MK-801-treated animals. PIDs associated with transient decreases of [Ca(2+)](o) were detected in suprasylvian gyri of only 4 vehicle-treated animals, of which 3 developed recurrent PIDs. Electrocorticogram was suppressed during PIDs, and electrocorticogram recovery worsened in a stepwise manner with consecutive depolarizations. PID duration increased slightly with ongoing ischemia and evolved to persistent depolarization at a final stage. NO transients were not detected during PID, and regional cerebral blood flow transients were not pronounced. Infarction was larger with initial persistent depolarization than with PID and was smallest in MK-801-treated animals. CONCLUSIONS: PID is not a common finding in peri-infarct zones in cats, and it is suppressed by the N:-methyl-D-aspartate antagonist MK-801. However, if repeated PIDs are generated, they result in a stepwise, progressive breakdown of neuronal function and ion homeostasis, probably contributing to the growth of infarction in focal cerebral ischemia. Recurrent Ca(2+) influx is a mechanism that presumably contributes to this process.

Animals↗

PubMed2001

Predictive value of neurochemical monitoring in large middle cerebral artery infarction.

BACKGROUND AND PURPOSE: Space-occupying brain edema is a life-threatening complication in patients with large hemispheric stroke. Early identification of patients at risk is necessary to decide on invasive therapies such as decompressive hemicraniectomy or hypothermia. To assess potential predictors of malignant brain edema by measurement of intracranial pressure (ICP) and microdialysis in patients with large hemispheric stroke and different clinical course. METHODS: In an ongoing prospective clinical study, an ICP and microdialysis probe were placed into the parenchyma of the ipsilateral frontal lobe of 10 patients. Extracellular concentrations of glutamate, lactate, pyruvate, and glycerol were measured continuously. Repeated cranial CT scans were scrutinized for size of infarction and presence of mass effect. RESULTS: The dynamics of the different substances varied in accordance with the clinical course, size of infarction, and local brain edema: Increase in ICP and in glutamate concentration and lactate-pyruvate ratio was followed by massive edema and large infarcts; generally low and stable ICP and substrate concentrations were found in patients without progressive space-occupying infarcts. CONCLUSIONS: In patients with large hemispheric infarction, bedside monitoring with microdialysis is feasible and might be helpful together with ICP recording to follow the development of malignant brain edema.

Adult↗

PubMed2001

Possible control of intermittent cerebral ischemia by monitoring of direct-current potentials.

OBJECT: Neurosurgically induced temporary occlusion of intracranial arteries carries the risk of cerebral ischemic damage. Because negative shifts in the cortical direct-current (DC) potential indicate tissue depolarization and, thus, critical ischemic stress, the authors hypothesized that recordings of these potentials could help to determine the optimal duration and frequency of induced intermittent focal ischemia to prevent brain injury. The investigators related the results of DC recordings both to simultaneously recorded decreases in extracellular Ca++ concentration ([Ca++]o), which reflect Ca++ entry into cells, and to histological outcome. METHODS: In cats anesthetized with halothane the effects of intermittent brief (10 minutes long, six times [6 x 10-min group]) and prolonged (20 minutes long, three times [3 x 20-min group]) episodes of middle cerebral artery occlusions were compared with those of a single continuous episode (1 x 60-min group). Laser Doppler flow probes and ion-selective microelectrodes were used to measure cerebral blood flow, DC potentials, and [Ca++]o in cortical tissues of ectosylvian gyri. Negative shifts in DC potential were evaluated in the three groups during the entire 60-minute-long period of ischemia and were smallest in the 6 x 10-min group, larger in the 3 x 20-min group, and largest in the 1 x 60-min group. Accordingly, infarct volumes were smallest in the 6 x 10-min group, intermediate in the 3 x 20-min group, and largest in the 1 x 60-min group. Decreases in ischemic [Ca++]o were significantly greater in the 1 x 60-min group than in the two groups in which there were repetitive occlusions, and recovery of [Ca++]o after reperfusion normalized only in the 1 x 60-min group. CONCLUSIONS: The DC potential may provide a reliable measure to optimize intermittent ischemia and to achieve minimal ischemic brain injury during temporary neurosurgical occlusion of cerebral arteries.

Animals↗

PubMed2001

Quantitative kinetics of [124I]FIAU in cat and man.

UNLABELLED: For the assessment of the efficacy of clinical gene therapy trials, different imaging modalities have been developed that enable a noninvasive assessment of location, magnitude, and duration of transduced gene expression in vivo. These imaging methods rely on a combination of an appropriate marker gene and a radiolabeled or paramagnetic marker substrate that can be detected by PET or MRI. Here, we assess whether the nucleoside analog 2'-fluoro-2'-deoxy-1beta-D-arabinofuranosyl-5-iodouracil (FIAU), a specific marker substrate for herpes simplex virus type 1 thymidine kinase (HSV-1-tk) gene expression, penetrates the blood-brain barrier (BBB) as an essential prerequisite for a noninvasive assessment of HSV-1-tk gene expression in gliomas. METHODS: No-carrier-added [(124)I]FIAU was synthesized by reacting the precursor 2'-fluoro-2'-deoxy-1beta-D-arabinofuranosyluracil (FAU) with carrier-free [(124)I]NaI. The course of biodistribution of [(124)I]FIAU was investigated in anesthetized cats (n = 3; organs) and in one patient with a recurrent glioblastoma (plasma and brain) by PET imaging over several hours (cats, 1-22 h) to several days (patient, 1-68 h). FIAU PET was performed in conjunction with multitracer PET imaging (cerebral blood flow and cerebral metabolic rate of O(2) in cats only; cerebral metabolic rate of glucose and [(11)C]methionine in all subjects). A region-of-interest analysis was performed on the basis of coregistered high-resolution MR images. The average radioactivity concentration was determined, decay corrected, and recalculated as percentage injected dose per gram of tissue (%ID/g) or as standardized uptake values (SUVs). RESULTS: The average chemical yield of [(124)I]FIAU synthesis was 54.6% +/- 6.8%. The chemical and radiochemical purities of [(124)I]FIAU were found to be >98% and >95%, respectively. In cats, the kinetic analysis of [(124)I]FIAU-derived radioactivity showed an early peak (1-2 min after injection) in heart and kidneys (0.20 %ID/g; SUV, 4.0) followed by a second peak (10-20 min after injection) in liver and spleen (0.16 %ID/g; SUV, 3.2) with subsequent clearance from tissues and a late peak in the bladder (10-15 h after injection). In the unlesioned cat brain, no substantial [(124)I]FIAU uptake occurred throughout the measurement (<0.02 %ID/g; SUV, <0.4). In the patient, [(124)I]FIAU uptake in normal brain was also very low (<0.0002 %ID/g; SUV, <0.16). In contrast, the recurrent glioblastoma revealed relatively high levels of [(124)I]FIAU-derived radioactivity (5-10 min after injection; 0.001 %ID/g; SUV, 0.8), which cleared slowly over the 68-h imaging period. CONCLUSION: The PET marker substrate FIAU does not penetrate the intact BBB significantly and, hence, is not the marker substrate of choice for the noninvasive localization of HSV-1-tk gene expression in the central nervous system under conditions in which the BBB is likely to be intact. However, substantial levels of [(124)I]FIAU-derived radioactivity may occur within areas of BBB disruption (e.g., glioblastoma), which is an essential prerequisite for imaging clinically relevant levels of HSV-1-tk gene expression in brain tumors after gene therapy by FIAU PET. For this purpose, washout of nonspecific radioactivity should be allowed for several days.

Animals↗

PubMed2000

Integrin-associated protein and thrombospondin-1 as endothelial mechanosensitive death mediators.

Recently, it was reported that the offset of hemodynamic forces induces an unusual pattern of apoptosis in vascular endothelium (1). Although the apoptotic trigger covers all cells and is maintained for a longer time period, only few cells become apoptotic. So, in contrast to common apoptosis inducers, the lack of hemodynamic forces initiates only a low basal level of apoptosis, however steadily increases with time, this way preventing the complete vessel destruction upon an only transient offset of blood flow. The molecular means by which the mechanical stimulus and apoptosis are smoothly coupled have now been identified as an autocrine loop of thrombospondin-1 (TSP-1) and the alpha(v)beta(3) integrin/integrin-associated protein (IAP) complex as its receptor. Vascular EC (EC) secrete TSP-1 only in postconfluent static monolayers and not under flow. This also holds true for the IAP whereas the alpha(v)beta(3) integrin is present under static conditions, as well as under flow, assigning the IAP an essential and new switch function in the receptor complex.

Antibodies, Monoclonal↗

PubMed2000

Sideband patterns from rotor-encoded longitudinal magnetization in MAS recoupling experiments.

Recent multiple-quantum MAS NMR experiments have shown that a change in the rotor phase (and, hence, in the Hamiltonian) between the excitation and reconversion periods can lead to informative spinning-sideband patterns. However, such "rotor encoding" is not limited to multiple-quantum experiments. Here it is shown that longitudinal magnetization can also be rotor-encoded. Both homonuclear and heteronuclear rotor encoding of longitudinal magnetization (RELM) experiments are performed on dipolar-coupled spin-1/2 systems, and the corresponding sideband patterns in the indirect dimension are analyzed. In both cases, only even-order sidebands are produced, and their intensity distribution depends on the durations of the recoupling periods. In heteronuclear experiments using REDOR-type recoupling, purely dipolar sideband patterns that are entirely free of effects due to the chemical-shielding anisotropy can be generated. Advantages and disadvantages of the heteronuclear RELM experiment are discussed in the context of other methods used to measure heteronuclear dipolar couplings.

Alanine↗