PubMed Health⌕ Search

Biomedical subjects

M R Lewis

Publications and source records attributed to M R Lewis.

At least 19 recordsLinked to original sources
PubMed1999

Comparison of four 64Cu-labeled somatostatin analogues in vitro and in a tumor-bearing rat model: evaluation of new derivatives for positron emission tomography imaging and targeted radiotherapy.

Previous studies have shown that modification of the somatostatin analogue octreotide (OC), by substitution of tyrosine for phenylalanine at position 3 and of a C-terminal carboxylic acid for an alcohol, to give Tyr3-octreotate (Y3-TATE) improved uptake of the peptide in somatostatin receptor-positive tissues. To determine which substitution best accounts for increased target tissue uptake, the peptides containing single modifications, Tyr3-octreotide (Y3-OC) and octreotate (TATE), were synthesized. These peptides were conjugated to the macrocyclic chelating agent 1,4,8, 11-tetraazacyclotetradecane-N,N',N",N"'-tetraacetic acid (TETA) and radiolabeled with 64Cu(II). The in vitro receptor binding, in vitro tumor cell uptake, and in vivo distribution properties of 64Cu-labeled TETA-Y3-OC and TETA-TATE were compared to those of [64Cu]TETA-OC and [64Cu]TETA-Y3-TATE. Cu-TETA-TATE (IC50 = 0.297 +/- 0.0055 nM) and Cu-TETA-Y3-TATE (IC50 = 0.308 +/- 0.0375 nM) displayed significantly higher binding affinity to somatostatin receptors on CA20948 rat pancreatic tumor membranes than Cu-TETA-Y3-OC (IC50 = 0.397 +/- 0.0206 nM) and Cu-TETA-OC (IC50 = 0. 498 +/- 0.039 nM). Similarly, the uptakes of [64Cu]TETA-Y3-TATE (60. 75 +/- 1.21%) and [64Cu]TETA-TATE (55.62 +/- 0.16%) into AR42J rat pancreatic tumor cells over a 2-h time period were higher than those of [64Cu]TETA-Y3-OC (47.20 +/- 1.20%) and [64Cu]TETA-OC (34.07 +/- 2. 24%). The in vitro results suggest that the C-terminal carboxylate may contribute more to enhanced receptor binding and tumor cell uptake than the substitution at the 3-position. Biodistributions in CA20948 tumor-bearing rats showed receptor-mediated uptake of the 64Cu-labeled peptides in somatostatin-rich tissues, including the pituitary, adrenals, pancreas, and tumor. The structure-activity relationships of the four 64Cu-labeled peptides did not show consistent trends in all target tissues, but [64Cu]TETA-Y3-TATE exhibited tumor uptake 1.75-3.5 times higher than the other derivatives at 4 h postinjection. The greater tumor retention of [64Cu]TETA-Y3-TATE justifies the selection of this agent for future PET imaging and targeted radiotherapy studies.

Adrenal Glands↗
PubMed1999

Quality assessment of atomic force microscopy probes by scanning electron microscopy: correlation of tip structure with rendered images.

While image quality from instruments such as electron microscopes, light microscopes, and confocal laser scanning microscopes is mostly influenced by the alignment of optical train components, the atomic force microscope differs in that image quality is highly dependent upon a consumable component, the scanning probe. Although many types of scanning probes are commercially available, specific configurations and styles are generally recommended for specific applications. For instance, in our area of interest, tapping mode imaging of biological constituents in fluid, double ended, oxide-sharpened pyramidal silicon nitride probes are most often employed. These cantilevers contain four differently sized probes; thick- and thin-legged 100 microm long and thick- and thin-legged 200 microm long, with only one probe used per cantilever. In a recent investigation [Taatjes et al. (1997) Cell Biol. Int. 21:715-726], we used the scanning electron microscope to modify the oxide-sharpened pyramidal probe by creating an electron beam deposited tip with a higher aspect ratio than unmodified tips. Placing the probes in the scanning electron microscope for modification prompted us to begin to examine the probes for defects both before and after use with the atomic force microscope. The most frequently encountered defect was a mis-centered probe, or a probe hanging off the end of the cantilever. If we had difficulty imaging with a probe, we would examine the probe in the scanning electron microscope to determine if any defects were present, or if the tip had become contaminated during scanning. Moreover, we observed that electron beam deposited tips were blunted by the act of scanning a hard specimen, such as colloidal gold with the atomic force microscope. We also present a mathematical geometric model for deducing the interaction between an electron beam deposited tip and either a spherical or elliptical specimen. Examination of probes in the scanning electron microscope may assist in interpreting images generated by the atomic force microscope.

DNA↗
PubMed1999

Antimicrobial activities of amine- and guanidine-functionalized cholic acid derivatives.

Compounds in a series of cholic acid derivatives, designed to mimic the activities of polymyxin B and its derivatives, act as both potent antibiotics and effective permeabilizers of the outer membranes of gram-negative bacteria. Some of these compounds rival polymyxin B in antibacterial activity against gram-negative bacteria and are also very active against gram-positive organisms. Other compounds interact synergistically with hydrophobic antibiotics to inhibit bacterial growth.

Anti-Bacterial Agents↗
PubMed1998

Three-dimensional crystals of Ca2+-ATPase from sarcoplasmic reticulum: merging electron diffraction tilt series and imaging the (h, k, 0) projection.

Electron crystallography offers an increasingly viable alternative to X-ray crystallography for structure determination, especially for membrane proteins. The methodology has been developed and successfully applied to 2D crystals; however, well-ordered thin, 3D crystals are often produced during crystallization trials and generally discarded due to complexities in structure analysis. To cope with these complexities, we have developed a general method for determining unit cell geometry and for merging electron diffraction data from tilt series. We have applied this method to thin, monoclinic crystals of Ca2+-ATPase from sarcoplasmic reticulum, thus characterizing the unit cell and generating a 3D set of electron diffraction amplitudes to 8 A resolution with tilt angles up to 30 degrees. The indexing of data from the tilt series has been verified by an analysis of Laue zones near the (h, k, 0) projection and the unit cell geometry is consistent with low-angle X-ray scattering from these crystals. Based on this unit cell geometry, we have systematically tilted crystals to record images of the (h, k, 0) projection. After averaging the corresponding phases to 8 A resolution, an (h, k, 0) projection map has been calculated by combining image phases with electron diffraction amplitudes. This map contains discrete densities that most likely correspond to Ca2+-ATPase dimers, unlike previous maps of untilted crystals in which molecules from successive layers are not aligned. Comparison with a projection structure from tubular crystals reveals differences that are likely due to the conformational change accompanying calcium binding to Ca2+-ATPase.

Calcium-Transporting ATPases↗
PubMed1998

Zinc gluconate: acute ingestion.

CASE REPORT: Despite the popularity of zinc gluconate for use in attenuation of common cold symptoms, there is little information on the effects of acute overdose. A 17-year-old male ingested approximately 85 tablets or 4 g zinc gluconate (570 mg elemental zinc). He experienced severe nausea and vomiting within 30 minutes of the ingestion but had no further sequelae such as diarrhea, gastric erosions, esophageal burns, shock, neurologic dysfunction, symptoms of anemia, or hepatic inflammation. Serum zinc level was 4.97 mg/dL at approximately 5 hours postingestion.

Administration, Oral↗
PubMed1994

Cryo-electron microscopy of deoxy-sickle hemoglobin fibers.

Deoxy-sickle hemoglobin (HbS) polymerizes in vivo into long helical fibers which fill the red cell and make it rigid. This impedes red cell passage through the capillaries and is responsible for the clinical manifestations of sickle cell disease. Images of individual and laterally associated HbS fibers were obtained by electron microscopy of frozen hydrated specimens. Each fiber possesses variable pitch, having from 6 degrees to 12 degrees rotation per unit cell. Laterally associated HbS fibers display systematic inter-fiber contacts in spite of their pitch variations, and exhibit better order than isolated fibers. This suggest that inter-fiber contacts can act to couple fibers mechanically and might therefore be a factor in rigidifying red cells in vivo. Fiber variability was attributed to local torsional variations with a standard deviation of 2.5 degrees, but which are weakly coupled over a length of 2.25 unit cells. Variable pitch produces structural changes of as large as 5 A azimuthally and 6 A axially in HbS fiber unit cells.

Cryopreservation↗
PubMed1994

Variable pitch in frozen-hydrated sickle hemoglobin fibers: an image analysis model study.

The intracellular polymerization of deoxyhemoglobin S (HbS) into helical fibers is the primary pathological event which gives rise to sickle cell disease. The structure of these fibers has previously been studied by electron microscopy of negatively stained specimens. We are extending these studies with unstained frozen-hydrated HbS fibers (cryo-EM), which afford better visualization of the internal details of the fiber structure than can be achieved by negative staining, but have lower signal-to-noise ratio images. The pitch of the HbS fiber structure varies locally along any given particle. Because rotation about the particle axis thus is partially decoupled from translation along the axis, the pitch and angular rotation of a fiber unit cell cannot be inferred by symmetry (as is the case with constant pitch helices). Image analysis procedures are presented which are capable of explicitly identifying the pitch and angular rotation of individual HbS fiber unit cells having low signal-to-noise ratios. Fiber images are divided into segments one unit cell long (63 A) which are analyzed in two steps. First each unit cell is aligned with constant pitch electron density reference models by cross-correlation. Correlation coefficients are then used to determine angular rotation and pitch. This procedure was tested, and found to be robust, using model images corrupted to simulate experimental problems normally encountered in the analysis of cryo-electron micrographs. The effects of limited resolution, low signal-to-noise ratio, scaling errors, and rotational and axial misalignment are described.

Computer Simulation↗
PubMed1992

Blood analysis.

Explore the source record for details and available documents.

Blood Chemical Analysis↗
PubMed1991

The hand of the helix of deoxyhemoglobin S fibers.

Electron micrographs of deoxyhemoglobin S fiber cross sections provide an end-on view of the fiber whose appearance is sensitive to small changes in orientation. We have developed a procedure to exploit this sensitivity in order to determine the hand of these particles. In a sickle hemoglobin fiber the hemoglobin molecules form long pitch helical strands which twist about the particle axis with a pitch of about 3000 A. Tilting a 400-A-thick cross section by a few degrees aligns one of the long pitch helices so that it is nearly parallel to the direction of view. When a strand of hemoglobin molecules in a fiber is aligned in this manner it appears as a strongly contrasted bright spot. It is this spot, rather than the fiber axis, which appears to be the apparent center of rotation of the cross section. The direction of the displacement of the spot from the particle axis depends upon the particle hand and tilt direction. We have used this property to determine that sickle hemoglobin fibers are right-handed particles. This method may be applicable to other particles with long pitch helices as well.

Computer Simulation↗
PubMed1989

Primary afferent excitatory transmission recorded intracellularly in vitro from rat medial vestibular neurons.

Intracellular recordings were made from rat medial vestibular nucleus (MVN) neurons in transverse brain slices containing the root of the vestibular nerve (N. VIII). Electrical stimuli applied to the N. VIII tract evoked an orthodromic excitatory postsynaptic potential (EPSP) that lasted about 50 ms following a 0.5 to 1.5 ms delay between the stimulus artifact and synaptic potential. These orthodromic EPSPs were insensitive to the following antagonists: atropine, hexamethonium, diphenhydramine, and caffeine. Based on these results we conclude that the primary afferent excitatory transmitter is not acetylcholine, histamine, or adenosine, respectively. However, kynurenic acid, a general excitatory amino acid receptor antagonist, blocked the orthodromic EPSP while having no effect on the resting membrane potential, input resistance, or action potential configuration of MVN neurons. Our data suggest that an excitatory amino acid, or amino acid-like substance, is responsible for primary afferent excitatory transmission in the rat medial vestibular nucleus.

Action Potentials↗
PubMed1988

Studies on Ca(II) binding to gamma-carboxyglutamic acid. Use of thermal decarboxylation to probe metal ion/gamma-carboxyglutamic acid interactions.

The thermal decarboxylation of N-benzyloxycarbonyl-L-gamma-carboxyglutamic acid alpha-methyl ester [Z)-L-Gla-OMe) has been studied. In the presence of increasing amounts of calcium or magnesium ions, lyophilized powders of (Z)-L-Gla-OMe exhibit a corresponding increase in thermal stability. Both magnesium and calcium form relatively tight, thermally stable complexes with (Z)-L-Gla-OMe at high metal ion concentrations. Differences between Ca(II) and Mg(II) binding are noted at low metal ion concentrations, where (Z)-L-Gla-OMe is in excess. Under these conditions, complex formation with Mg(II) apparently favors a 2:1 Gla-magnesium ion complex in which both Gla residues are unstable to thermal decarboxylation. Calcium ion complexes, however, are found to favor a 3:1 Gla-calcium ion complex in which 1 of the 3 Gla residues is thermally stable.

1-Carboxyglutamic Acid↗
PubMed1987

An in vitro brain slice preparation to study the pharmacology of central vestibular neurons.

The purpose for development of this preparation was to allow detailed studies of the pharmacological and electrophysiological properties of individual central vestibular neurons. The pharmacology of the central afferent synapses of the vestibular system has not been examined at the level of the neuronal membrane, and as a result few definitive reports are available. The best studies have used in situ extracellular recording techniques that are difficult to interpret. For instance, recent literature still supports the concept that excitatory transmission at the N. VIII to vestibular nuclei synapse is cholinergic. Our data refute this hypothesis and suggest that an excitatory amino acid is the most likely candidate for the eighth nerve to medial vestibular nucleus in the rat. We believe this preparation combined with an intracellular electrophysiological approach will shed information of value to both the basic scientist and the clinician with interest in the vestibular system.

Action Potentials↗
PubMed1987

Mechanisms underlying the antimotion sickness effects of psychostimulants.

The major conclusions of this review are: 1) that selective enhancement of dopaminergic transmission, not noradrenergic, is sufficient to account for amphetamine-induced resistance and perhaps natural resistance to motion sickness; 2) the site of this enhanced dopaminergic transmission is probably within the basal ganglia; and 3) the neuropharmacology of the basal ganglia, but not the brainstem vestibular areas, can account for the therapeutic synergism of scopolamine and amphetamine. The therapeutic actions of psychostimulants may be dissociable from some of their side effects, particularly cardiovascular effects related to peripheral norepinephrine release. Drugs which target specific subtypes of dopaminergic receptors may serve this purpose.

Amphetamine↗
PubMed1986

The swollen leg.

Explore the source record for details and available documents.

Diagnosis, Differential↗