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Biomedical subjects

A Haase

Publications and source records attributed to A Haase.

At least 145 records · Page 8Linked to original sources
PubMed1994

Investigation of the 1H NMR visibility of lactate in different rat and human brain cells.

In recent years, 1H MRS has been used in a number of studies to measure the lactate content of brain, and it is generally assumed that the methyl resonance at 1.3 ppm reflects the total amount of lactate present in the tissue. However, reduced NMR visibility of lactate has recently been reported for blood, heart and skeletal muscle as well as for bacteria. We have assessed the NMR visibility of lactate in cultures of human and rat brain cells, comparing the concentrations measured by NMR and by biochemical methods. Contributions of fatty acids have been eliminated using their different relaxation behavior. We found approximately 30% of the lactate to be undetectable by NMR in the studied cell cultures. While the mechanism partially masking lactate in 1H spectra is not yet understood, the potential invisibility of some pools of lactate to NMR may greatly affect the interpretation of brain spectra.

Animals↗
PubMed1994

Fast 19F-NMR imaging in vivo using FLASH-MRI.

The goal of this study was the development of a method that allows the acquisition of chemical shift selective 19F NMR images within a short measuring time. A train of small tip angle frequency selective pulses, each followed by a dephasing gradient of random strength, was used as a presaturation experiment for the suppression of the unwanted chemical shift components. Imaging was performed after presaturation using a SNAPSHOT-FLASH experiment. The acquisition time for a 64 x 128 image including the presaturation experiment amounted to only 470 ms. The sequence was applied in a 4.7 Tesla magnet to perform a longitudinal pharmacological study on the clearance of perfluoroocytlbromide (PFOB) in the liver and spleen of rats.

Animals↗
PubMed1994

Streptokinase alleles and disease association in group A streptococci.

Allele-specific oligonucleotides were used for PCR-based typing of the streptokinase locus of group A streptococcal strains, including well characterized type strains, isolates from patients with acute poststreptococcal glomerulonephritis and strains from Aboriginal communities in the Northern Territory of Australia. The streptokinase SKN allele, previously thought to be associated with glomerulonephritis, was no more frequent in nephritogenic than in non-nephritogenic streptococcal strains in this collection.

Alleles↗
PubMed1994

Phospholipid analogues: side chain- and polar head group-dependent effects on phosphatidylcholine biosynthesis.

In recent studies we showed that the phospholipid analogue hexadecylphosphocholine inhibits phosphatidylcholine biosynthesis by affecting the translocation of the rate-limiting enzyme of phosphatidylcholine biosynthesis, CTP:phosphocholine cytidylyltransferase (EC 2.7.7.15), to membranes, where it is active (Geilen et al. 1992. J. Biol. Chem. 267: 6719-6724). The present study was performed to investigate the structure-dependency of this effect. It is shown that the inhibitory properties of phospholipid analogues are dependent on their alkyl side chain length (dodecylphosphocholine < tetradecylphosphocholine < hexadecylphosphocholine < heptadecylphosphocholine < octadecylphosphocholine > eicosadecylphosphocholine). Furthermore, it is demonstrated that this inhibition of phosphatidylcholine biosynthesis by phospholipid analogues is also dependent on the polar head group (hexadecylphosphocholine >> hexadecylphosphoethanolamine = hexadecylphosphoserine). These effects result from an inhibition of the CTP:phosphocholine cytidylyltransferase and are not due to an inhibition of choline uptake or differences in the cellular uptake of the phospholipid analogues investigated.

Animals↗
PubMed1994

[Reduction of NMR image artefacts by using optimal materials as diagnostic aids and implants].

Differences in magnetic susceptibility, as occur for example at the boundary between implant materials and the surrounding body tissue, result in artefacts and a signal loss in magnetic resonance imaging. By using materials with a magnetic susceptibility matched to the respective environment, it is possible to minimize both artefacts and signal loss. Such materials can be made by combining two materials of different magnetic susceptibility (e.g. diamagnetic and paramagnetic materials) in such a way that the resulting material has the desired effective magnetic susceptibility.

Artifacts↗
PubMed1993

Quantification of regional blood volumes by rapid T1 mapping.

A new method is presented for the quantitative determination of regional blood volumes in vivo. It is based on rapid quantitative T1 mapping by Snapshot FLASH MRI combined with the injection of an intravascular MR contrast agent. Regional blood volumes in four different tissues of the rat (skeletal muscle, heart, liver, kidney) were determined in an in vivo experiment.

Animals↗
PubMed1993

Magnetic resonance imaging investigation of blood-brain barrier damage in adoptive transfer experimental autoimmune encephalomyelitis.

Recent advances in fast magnetic resonance imaging (MRI) techniques have allowed quantification of parameters such as T1 relaxation time, which can be modified by changes in the water content of a tissue. We have used this new method to study the evolution of blood-brain barrier (BBB) changes after adoptive transfer of MBP-specific (AT-EAE) and ovalbumin-specific T cell lines in Lewis rats. Measurable changes in T1 relaxation time suggesting widespread increase in BBB permeability were found, starting on day 3 post inoculation (p.i.), in the midbrain and brainstem of AT-EAE rats. In addition, we noted a significant decrease in T1 relaxation time before injection of a paramagnetic agent, in the cisternal cerebrospinal fluid (CSF) of diseased animals, starting on day 5 p.i. In vitro measurement of T1 in CSF containing various concentrations of albumin, IgM and glucose showed that, at physiological concentrations, a T1 decrease is mainly associated with an increase in albumin concentration. A moderate increase in BBB and blood-CSF barrier permeability was found as early as 4-8 h p.i., in rats injected with MBP-specific as in animals injected with ovalbumin-specific T cell lines, suggesting a non-specific mechanism. Experimental MRI may become a powerful tool to sequentially analyse changes in barrier dynamics, for example following pharmacological intervention.

Animals↗
PubMed1993

Repeat unit polysaccharides of bacteria: a model for polymerization resembling that of ribosomes and fatty acid synthetase, with a novel mechanism for determining chain length.

We report the identification and sequence from Escherichia coli and Salmonella enterica strains of the cld gene, encoding the chain-length determinant (CLD) which confers a modal distribution of chain length on the O-antigen component of lipopolysaccharide (LPS). The distribution of chain lengths in the absence of this gene fits a model in which as the chain is extended there is a constant probability of 0.165 of transfer of growing chain to LPS core, with termination of chain extension. The data for E. coli O111 fit a model in which the CLD reduces this probability for short chains and increases it to 0.4 for longer chains, leading to a reduced number of short chain molecules but an increase in numbers of longer molecules and transfer of essentially all molecules by chain length 21. We put forward a model for O-antigen polymerase which resembles the ribosome and fatty acid synthetase in having two sites, with the growing chain being transferred from a D site onto the new unit at the R site to extend the chain and then back to the D site to repeat the process. It is proposed that the CLD protein and polymerase form a complex which has two states: 'E' facilitating extension and 'T' facilitating transfer to core. The complex is postulated to enter the E state as O-antigen polymerization starts, and to shift to the T state after a predetermined time, the CLD acting as a molecular clock. The CLD is not O-antigen or species-specific but the modal value does depend on the source of the cld gene.

Amino Acid Sequence↗
PubMed1993

Molecular analysis of the 3,6-dideoxyhexose pathway genes of Yersinia pseudotuberculosis serogroup IIA.

Salmonella enterica and Yersinia pseudotuberculosis are the only examples in nature known to use a variety of 3,6-dideoxyhexose derivatives as O antigen constituents. To allow a comparison of the responsible biosynthetic genes of the two organisms, we have sequenced a section of the Y. pseudotuberculosis serogroup IIA rfb region that contained the genes for the abequose biosynthetic pathway. Comparison of the identified genes with the rfb region of S. enterica LT2 showed that the two dideoxyhexose pathway gene clusters are related. The arrangement of the genes was largely conserved, and the G + C compositions of the two DNA regions were strikingly similar; however, the degree of conservation of nucleotide and protein sequences suggested that the two gene clusters have been evolving independently for considerable time. Hybridization experiments showed that the dideoxyhexose pathway genes are widespread throughout the various serogroups of Y. pseudotuberculosis.

Amino Acid Sequence↗
PubMed1992

A new in situ hybridization technique for spliced RNA species documents the bone marrow origin of pulmonary macrophages in chronic myelogenous leukemia.

Tissue macrophages derive from monocytes of bone marrow origin. Because monocytes from patients with chronic myelogenous leukemia (CML) contain the Philadelphia chromosome (Ph), it seemed probable that tissue macrophages in CML would originate from the malignant clone. Using powerful molecular techniques, we studied pulmonary alveolar macrophages (PAM) from two patients with CML. PAM from Patient 1, a patient in chronic phase studied before bone marrow transplantation (BMT), contained the Ph by Southern blot analysis. Patient 2, an accelerated phase patient, was studied after post-BMT relapse. PAM from this patient not only contained the Ph, but also expressed the BCR/ABL message documented by a new splice junction in situ hybridization technique. This new technique allows detection of BCR/ABL mRNA and determination of splice useage in individual cells. These data confirm the continued replenishing of PAM from peripheral blood monocytes in non-BMT settings and represent the first direct evidence that tissue macrophages are derived from the malignant clone in patients with CML.

Adult↗
PubMed1992

Scan time reduction in snapshot FLASH MRI.

We describe the speeding up of snapshot FLASH MRI by placing a slice selection experiment before the whole imaging sequence. In conventional snapshot FLASH slice selection is made in every projection, thus consuming a great deal of experimental time. This problem can be overcome by applying only one slice-selective procedure before starting the imaging. The idea is to make a selective saturation of the outer volume and to interrogate the unaffected slice by a train of rapid, hard, low-angle pulses. By this new method the measuring times of snapshot FLASH can be further reduced.

Abdomen↗
PubMed1992

Direct measurement of spin-lattice relaxation times of phosphorus metabolites in human myocardium.

T1 values of phosphorus metabolites visible in human cardiac 31P-MR spectra were determined in 12 volunteers at 1.5 T. Consecutive spectra were acquired with varying pulse repetition time (TR) from 1.6 to 24 s; volume selection was achieved with ISIS. T1's of creatine phosphate (CP), [gamma-P], [alpha-P], and [beta-P]ATP, 2-3 diphosphoglycerate, and phosphodiesters were 6.1 +/- 0.5, 5.4 +/- 0.5, 5.5 +/- 0.5, 5.8 +/- 1.0, 7.6 +/- 1.0, and 5.0 +/- 1.0 s, respectively. CP/ATP ratios showed little change with varying TR; linear regression of CP/ATP vs TR was of borderline significance (r = 0.28, P = 0.06). T1's for CP and ATP were also determined in standard solution (20 mM CP, 10 mM ATP) yielding T1CP of 8.7 +/- 0.2 and T1[gamma-P]-ATP of 9.9 +/- 0.7 s. Thus, T1's for CP and ATP were similar at 1.5 T in both human heart and standard solution. In human cardiac 31P-MR spectra, CP/ATP ratios may need little correction for partial saturation.

2,3-Diphosphoglycerate↗
PubMed1992

Human T-lymphotropic virus type I-associated myelopathy in patients with the acquired immunodeficiency syndrome.

We describe two cases of serologically confirmed human T-lymphotropic virus type I (HTLV-I)-associated myelopathy involving North American men coinfected by the human immunodeficiency virus type 1. Our first patient suffered from a gradually progressive spastic paraparesis for 10 years prior to presenting with Kaposi's sarcoma, while our second patient developed subacutely progressive spastic paraparesis in the setting of full-blown acquired immunodeficiency syndrome. Autopsy examination of the spinal cords from these two cases revealed widespread axonal loss and demyelination principally involving the lateral columns of case no. 1 and the lateral and anterior columns of case no. 2. Vascular sclerosis and hyalinization were prominent in both cases, but in neither was there a conspicuous inflammatory component. In case no. 2, HTLV-I mRNA was not detected by in situ hybridization, but HTLV-I proviral DNA sequences were detected in this case by polymerase chain reaction. Neither case exhibited multinucleated cell (human immunodeficiency virus type 1) myelitis, vacuolar myelopathy, or evidence of HTLV-II infection by polymerase chain reaction assay.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Fast inversion recovery T1 contrast and chemical shift contrast in high-resolution snapshot FLASH MR images.

Fast MR imaging attracts the interest of both clinicians and physicists because new diagnostic information arises with reduced artifacts due to short investigational times. With the acceleration of the Snapshot FLASH MR sequence, the measurement of high-resolution images with 256 x 256 matrix is reported, together with contrasting prepulses that are applied to attain contrast in combination with higher in-plane resolution. Measuring times are in the range of a second. For whole-body imaging, a TR = 5.2 msec and a TE = 2.6 msec could be attained measuring omit 256 x 256 matrix images. Artifact-free images demonstrating T1 contrast and contrast from chemical shift are performed on moving organs (heart, intestine) in different experiments. These applications can easily be performed in a couple of minutes for clinical use. Especially in the lung, short TE and high resolution result in a new imaging quality of pulmonary and mediastinal vessels.

Abdomen↗
PubMed1992

Radial Turgor and Osmotic Pressure Profiles in Intact and Excised Roots of Aster tripolium: Pressure Probe Measurements and Nuclear Magnetic Resonance-Imaging Analysis.

High-resolution nuclear magnetic resonance images (using very short spin-echo times of 3.8 milliseconds) of cross-sections of excised roots of the halophyte Aster tripolium showed radial cell strands separated by air-filled spaces. Radial insertion of the pressure probe (along the cell strands) into roots of intact plants revealed a marked increase of the turgor pressure from the outermost to the sixth cortical layer (from about 0.1-0.6 megapascals). Corresponding measurements of intracellular osmotic pressure in individual cortical cells (by means of a nanoliter osmometer) showed an osmotic pressure gradient of equal magnitude to the turgor pressure. Neither gradient changed significantly when the plants were grown in, or exposed for 1 hour to, media of high salinity. Differences were recorded in the ability of salts and nonelectrolytes to penetrate the apoplast in the root. The reflection coefficients of the cortical cells were approximately 1 for all the solutes tested. Excision of the root from the stem resulted in a collapse of the turgor and osmotic pressure gradients. After about 15 to 30 minutes, the turgor pressure throughout the cortex attained an intermediate (quasistationary) level of about 0.3 megapascals. This value agreed well with the osmotic value deduced from plasmolysis experiments on excised root segments. These and other data provided conclusions about the driving forces for water and solute transport in the roots and about the function of the air-filled radial spaces in water transport. They also showed that excised roots may be artifactual systems.

Journal Article↗
PubMed1992

Increased steady-state levels of alpha-fetoprotein mRNA in hepatocellular carcinoma: an analysis by in situ hybridization.

The molecular basis for the augmented production of alpha-fetoprotein is unknown. We have used in situ hybridization of alpha-fetoprotein cDNA to malignant hepatocytes to establish if increased serum alpha-fetoprotein concentrations are related to detectable steady-state levels of alpha-fetoprotein mRNA in hepatocytes. Tumor tissue from four patients with histologically confirmed hepatocellular carcinoma were examined, and the results compared to fetal liver. Northern blot hybridization for alpha-fetoprotein mRNA in tumor tissue was also analyzed. As expected a high number of grains was observed in fetal liver tissue, indicative of high levels of alpha-fetoprotein mRNA physiologically present during pre-natal development. Sections from all patients with high serum concentrations of alpha fetoprotein showed appreciable hybrid formation, which correlated semi-quantitatively with the serum concentrations. However, hybrids were not detected in a patient with a normal serum alpha-fetoprotein. The high alpha-fetoprotein mRNA levels in fetal and neoplastic liver suggest that gene transcription is the mechanism of alpha-fetoprotein production in malignancy, although the control of this mechanism remains speculative.

Adult↗
PubMed1992

A skin MR-marker for radiation treatment planning.

After experiences with fluid filled tubes a gel fitted with an adhesive has been developed, to reproducibly markate treatment ports on the patient's skin. A gel is chosen, that hinders loss of the fluid and smoothly fits to the skin surface due to the adhesive. The clinical use of the gel hopefully will help with the use of NMR image information in radiotherapy treatment planning.

Equipment Design↗