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Biomedical subjects

R R Walters

Publications and source records attributed to R R Walters.

At least 19 recordsLinked to original sources
PubMed1995

Assay of the enantiomers of ibutilide and artilide using solid-phase extraction, derivatization, and achiral-chiral column-switching high-performance liquid chromatography.

Ibutilide fumarate and artilide fumarate, new drugs for the treatment of cardiac arrhythmias, each contain a stereogenic center bearing a secondary alcohol group. Reversed-phase achiral-chiral column-switching HPLC separations of the enantiomers of each compound were developed and validated for quantitation in plasma and other biofluids. The key component of the method was derivatization with 1-naphthyl isocyanate, which enhanced the sensitivity of fluorescence detection and enabled the enantiomers to be separated on a Pirkle column (covalent 3,5-dinitrobenzoyl-D-phenylglycine stationary phase). The lower limit of quantitation of ibutilide fumarate was typically 0.1 ng/ml or less of each enantiomer in 1 ml of plasma. Two of the special features of the column-switching system included operation with two samples in the system at one time, which reduced analysis time to 16 min/sample for ibutilide and 19 min/sample for artilide, and a relay-operated switching of detector outputs, which allowed achiral and chiral column chromatographic data to be gathered from two detectors into a single data acquisition channel.

Anti-Arrhythmia Agents↗
PubMed1995

Continuous administration decreases and pulsatile administration increases behavioral sensitivity to a novel dopamine D2 agonist (U-91356A) in MPTP-exposed monkeys.

We compared the behavioral effects of a novel and highly selective dopamine D2 receptor agonist, U-91356A, administered to 6 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-exposed parkinsonian monkeys for 27 days following an intermittent (n = 3) or continuous (n = 3) schedule, using subcutaneous osmotic minipumps for the latter group. Each group received equivalent amount of drug daily. Dopamine D1 and D2 receptor binding assays were performed on striatal tissue homogenates with tritiated selective antagonists and were compared with those of 3 healthy control animals and 3 MPTP-exposed monkeys treated in parallel with daily doses of levodopa and 2 additional MPTP-exposed monkeys otherwise untreated. U-91356A quickly relieved all parkinsonian features and greatly stimulated locomotion in all animals. The pulsatile administration group showed progressive sensitization to the drug, and all 3 animals developed chorea during the first week of treatment that subsequently increased in intensity. The same pattern was seen in the levodopa-treated animals. In contrast, an apparent, incomplete tachyphylaxis were observed in 2 of 3 animals in the continuous infusion group during the first 10 days of treatment. Only 1 of these animals developed minimal and transient choreic dyskinesia. An apparent decrease of D2 receptor binding was observed. No upregulation of dopamine receptors occurred in the dyskinetic monkeys of the pulsatile group, but a tendency toward upregulation of putaminal D1 receptors was observed in the levodopa-treated, dyskinetic animals. These results confirm that the mode of administration of dopaminergic agents may result in a markedly different clinical outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoquinolines↗
PubMed1994

Chiral assay methods for lifibrol and metabolites in plasma and the observation of unidirectional chiral inversion following administration of the enantiomers to dogs.

Lifibrol, a new drug for the treatment of hypercholesterolemia, contains a stereogenic center bearing a secondary alcohol group. A normal-phase achiral-chiral HPLC separation of the enantiomers of lifibrol and two of its metabolites was developed and validated for quantitation in dog plasma. A silica and a Chiralcel OD-H column were operated in series and all six enantiomeric components and internal standard were directly separated. An initial solid-phase extraction (phenyl) clean-up step and a column-switching step to eliminate late-eluting compounds were also utilized. The solid-phase extraction step was automated using a robotic system. Assay development, validation, and application of the method to a bioavailability study of the racemate and enantiomers of lifibrol in dogs are described. The lower limit of quantitation was 0.0125 microgram/ml for each enantiomer of lifibrol using 200 microliters of dog plasma with UV detection (255 nm). In dog plasma following oral or intravenous administration of the racemate, the (R)/(S) ratio of the enantiomers of lifibrol was greater than one and increased with time. Following administration of the individual enantiomers, chiral inversion of the (S)-enantiomer but not the (R)-enantiomer was observed.

Administration, Oral↗
PubMed1993

Medicinal chemistry of imidazoquinolinone dopamine receptor agonists.

(R)-5-(Dipropylamino)-5,6-dihydro-4H-imidazo[4,5,1-ij]-quinolin-2( 1H)-on e (1a, U-86170), a potent high intrinsic activity dopamine (D2) agonist, has been prepared in eleven steps from quinoline. In several tests, the compound showed dopamine autoreceptor agonist activity at low doses. It showed postsynaptic agonist activity at somewhat higher doses, reversing the effects of reserpine in mice and increasing striatal acetylcholine levels. The compound showed some serotonergic (5HT1A) activity, but was inactive at other receptors. The related monopropylamine 2 (U-91356), also showed good dopaminergic agonist activity, and had improved metabolic stability and oral bioavailability in the rat and monkey when compared to 1a. Compounds 1a and 2 have been prepared in tritiated form, and [3H]1a (69 Ci/mmol) has found use as a D2 agonist radioligand in binding assays. The dopaminergic (D2) and serotonergic (5HT1A) activities of a series of compounds related to 1a have been evaluated using this ligand, [3H]raclopride, and [3H]8-OH DPAT.

Aminoquinolines↗
PubMed1992

Racemization and intramolecular nucleophilic substitution reactions of ibutilide.

The kinetics and mechanisms of the racemization and cyclization reactions of ibutilide are described. The cyclization reaction yields a bell-shaped rate-pH curve consistent with a change in rate-determining step. It is hypothesized that the hydroxyl group leaves to form a carbocation intermediate; this is followed by nucleophilic attack by the amine. This mechanism is supported by kinetic analysis, aniline trapping of carbocation intermediate, and observation of all four stereo-isomers of the resulting quaternary ammonium compound. Whereas racemization can also progress through the carbocation intermediate, a direct SN2 mechanism appears to be the major route for the racemization reaction.

Anti-Arrhythmia Agents↗
PubMed1989

Production, characterization, and utility of monoclonal antibodies which react with a novel chimeric glycoprotein of human respiratory syncytial virus termed FG.

Primary immunization of mice with recombinant vaccinia virus expressing the F or G glycoprotein of human respiratory syncytial virus followed by an intravenous boost with crude FG chimeric glycoprotein resulted in the generation of hybridomas each specific for either the F or G portion of FG. Characterization of each MAb was determined following binding to various viral and glycoprotein antigens, by immunoprecipitation, by competition binding and by subclass determination. Relative affinity was determined for each MAb following inhibition of binding by ammonium thiocyanate.

Animals↗
PubMed1989

Protection of cotton rats against human respiratory syncytial virus by vaccination with a novel chimeric FG glycoprotein.

The cotton rat model of experimental human respiratory syncytial virus (RSV) infection was used to study the efficacy of FG, a novel chimeric glycoprotein which was expressed in insect cells using a baculovirus vector. FG contained the extracellular regions of the F (fusion) and G (attachment) glycoproteins of RSV. Vaccination with FG resulted in induction of neutralizing antibody and was correlated with protection of lung tissue from RSV challenge against both serogroup A and B virus strains. Both crude FG taken from supernatants of insect cells and affinity-purified FG were immunogenic and active against RSV. FG vaccination was effective by three routes of administration, following a single dose, and when administered with different adjuvants.

Adjuvants, Immunologic↗
PubMed1988

Protein immobilization on silica supports. A ligand density study.

The immobilization of proteins on diol-bonded silica matrices containing carboxyl groups (spacer arms) was studied. It was found that the activated ester coupling method worked best with N,N'-dicyclohexylcarbodiimide as the condensing agent in the activation step. During protein coupling, the amount of protein immobilized was highest below pH 6. The optimum pore size of the silica was 300-1000 A. The spacer arm ligand density was varied over as much as a 100-fold range and the effects on the total activities and specific activities of several proteins were studied. Two proteins exhibited up to two-fold increases in specific activity at low ligand densities. However, the total amounts of activity and protein immobilized decreased at low ligand densities.

Hydrogen-Ion Concentration↗
PubMed1988

Lineage heterogeneity in acute leukemia with the t(4;11) abnormality: implications for acute mixed lineage leukemia.

Acute leukemia associated with the t(4;11)(q21;q23) abnormality demonstrates marked lineage heterogeneity, including cases with features of acute mixed lineage leukemia. We report 7 patients with acute leukemia with the t(4;11) abnormality in which we have defined the range of lineage commitment associated with this disease utilizing a variety of cell characterization techniques. Each case could be classified either as acute lymphoblastic leukemia (ALL) (5 cases) or acute myelogenous leukemia (AML) (2 cases) based on standard light microscopic criteria supplemented by ultrastructural determination of myeloperoxidase. Evidence for acute mixed lineage leukemia was found in one of the AML patients in which coexpression of CD14 and CD19 surface antigens was demonstrated. Overall, the findings further confirm the lineage heterogeneity previously reported in association with t(4;11) acute leukemia. The implications of the findings as to the pathogenesis of t(4;11) acute leukemia are discussed.

Adult↗
PubMed1987

A kinetic, chromatographic method for studying protein hydrodynamic behavior.

A chromatographic method based on "split-peak" behavior was described for the determination of the coefficient of mass transfer of proteins on small reversed-phase columns. The coefficient of mass transfer was found to be a linear function of the protein translational diffusion coefficient and inversely proportional to the square of the support particle diameter, as predicted by chromatographic theory. As an example of the practical application of this method for the measurement of protein diffusion coefficients, the denaturation of bovine serum albumin with decreasing solution pH was followed by measuring the change in the coefficient of mass transfer. A major advantage of this method was that the results were not affected by the interaction of the protein with the stationary phase.

Animals↗
PubMed1987

Dual-column determination of albumin and immunoglobulin G in serum by high-performance affinity chromatography.

High-performance affinity chromatography was used for the simultaneous determination of albumin and immunoglobulin G in serum. Two columns in series, the first containing immobilized anti-albumin antibodies and the other containing protein A for binding immunoglobulin G, were eluted separately at pH 3 by means of a column-switching system. This method gave results in good agreement with commercially available methods, while requiring only 2 microliter of serum and 6.0 min per cycle. It was shown that albumin and immunoglobulin G were selectively retained, with little interference from other components, including immunoglobulins A and M.

Chromatography, Affinity↗
PubMed1985

Affinity chromatographic examination of a retention model for macromolecules.

Plots of log k' vs. log (1/[mobile phase modifier]) were made for a monovalent and a divalent solute using affinity chromatography. Some of the plots were curved and all exhibited slopes (Z values) of less than the theoretical integer values. It was shown that this was an expected result when lower forms of the solute were present, e.g., a divalent solute adsorbed monovalently.

Chromatography, Affinity↗
PubMed1984

Protein separations on reversed-phase high-performance liquid chromatography minicolumns.

The resolution of cytochrome c, bovine serum albumin and ovalbumin on reversed-phase columns under gradient elution conditions was found to be constant or to improve as column length was decreased from 45 to 6.3 mm. The resolution remained constant even when the column length decreased to 1.6 mm. Recovery of protein in the first gradient cycle was improved by the use of short columns.

Animals↗
PubMed1984

Protein diffusion coefficient measurements by laminar flow analysis: method and applications.

Laminar flow in an open tube leads to solute band spreading. This process is opposed by radial diffusion. The translational diffusion coefficient of a solute can be calculated from the band dispersion, tube length, and flow rate. No calibration is necessary. A simple apparatus was used to measure the diffusion coefficients of several small solutes and 18 proteins. Most results were within +/- 10% of literature values. Each determination required 7-90 min, depending on the magnitude of the diffusion coefficient. The amount of protein needed was approximately 25 micrograms. The diffusion coefficient data were useful for the estimation of molecular weights.

Chemical Phenomena↗
PubMed1983

Determination of immunoglobulins in blood serum by high-performance affinity chromatography.

High-performance affinity chromatography columns were prepared by immobilizing protein A from Staphylococcus aureus on 10-microns diol-bonded silica. Immunoglobulin-containing samples were injected into the column at pH 7 and eluted by stepwise changes to pH 3. Immunoglobulin G, A, and M standards were tested, but only a small fraction of the latter two was retained on the column. Analysis of 3-microliters samples of reference blood sera without pretreatment was performed using immunoglobulin G standards. Good agreement was observed between the immunoglobulin G concentrations measured by this method and by radial immunodiffusion. Chromatography of albumin and electrophoresis of retained serum fractions showed no interference by non-specific adsorption. Chromatographic analysis times were 4 min or less.

Chromatography, Affinity↗