Biomedical subjects

T F Greber

Publications and source records attributed to T F Greber.

11 recordsLinked to original sources

PubMed1995

The development and cross-validation of methods based on radioimmunoassay and LC/MS-MS for the quantification of the class III antiarrhythmic agent, MK-0499, in human plasma and urine.

An analytical method based on radioimmunoassay (RIA) has been developed for the determination of the antiarrhythmic agent, MK-0499, in plasma and urine. Owing to the potency of the drug, the specificity of this assay in human plasma could not be adequately determined using conventional RIA procedures. A highly specific procedure, based on LC/MS-MS, was developed to cross-validate the RIA. The lower quantifiable limits of the RIA and LC/MS-MS-based methods were 0.05 and 0.013 ng ml-1, respectively. Cross-validation data, compared using paired student's t-test regression analysis, showed excellent correlation between methods. The mass spectrometric assay was also used to simultaneously measure plasma concentrations of unlabeled and 14C-labeled MK-0499 following administration of the drug at high specific activity to volunteers.

Animals↗

PubMed1994

A rapid and specific assay, based on liquid chromatography-atmospheric pressure chemical ionization mass spectrometry, for the determination of MK-434 (a 5 alpha-reductase inhibitor) and its metabolites in plasma.

MK-434 is a new 5 alpha-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography-mass spectrometry (LC-MS) has been developed for the determination of this compound in plasma. The analyte was isolated from plasma by solid-phase extraction on a C18 cartridge. A related substance, L-654,066, was used as the internal standard. Extracts were separated on a 5-cm C18-reversed-phase high performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion MS-MS mode. The method had sufficient sensitivity, precision, accuracy, and selectivity for the analysis of clinical samples containing MK-434 and its two principal metabolites at concentrations in the range 0.5-50 ng ml-1. The chromatographic run time was < 5 min.

5-alpha Reductase Inhibitors↗

PubMed1994

Determination of L-691,121, a new class III antiarrhythmic, and its principal metabolite in plasma by differential radioimmunoassay.

A sensitive and specific method based on radioimmunoassay (RIA) has been developed for the analysis of L-691,121, a new antiarrhythmic agent, and its major metabolite, L-692,199, in plasma. Two RIAs using immunogens and radioligands prepared from different derivatives of L-691,121 were used in conjunction to determine both parent compound and metabolite concentrations by solving simultaneous equations, since neither assay alone was adequately specific. Variable cross-reactivity factors were incorporated into the calculations to correct for non-parallel drug and metabolite displacement curves. The direct assay using 30 microliters of plasma is sensitive to 0.1 ng ml-1 and has sufficient precision, accuracy and specificity for the analysis of clinical samples.

Animals↗

PubMed1992

Determination of L-654,066, a new 5 alpha-reductase inhibitor in plasma by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry.

L-654,066 is a new 5 alpha-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography/mass spectrometry has been developed for the determination of this drug candidate in plasma. The analyte was isolated from plasma by solid-phase extraction on a C-18 cartridge. A related substance, L-683,838, was used as the internal standard. Extracts were chromatographed on a 5 cm C18 reverse-phase high-performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion tandem mode. The method has sufficient sensitivity, precision, accuracy and selectivity for the analysis of clinical samples containing L-654,066 at concentrations in the range 0.5-20 ng ml-1. The chromatographic run time is less than 2 min.

Azasteroids↗

PubMed1990

A radioimmunoassay for the anticonvulsant and neuroprotective agent, MK-801.

A radioimmunoassay is described for MK-801, a potent anticonvulsant and neuroprotective agent. Two immunogens were prepared from N-glutaryl- and N-carboxyethyl-MK-801 by coupling through their carboxyl groups to bovine serum albumin. Radioligands were I-125-iodotyramine conjugates of the same derivatives. Both types of antisera displayed bridge recognition which could be circumvented. In the first case, specificity for N-acyl derivatives was satisfied by acetylating the analyte prior to measurement. Antisera to the N-alkyl derivative yielded a satisfactory assay for MK-801 when the heterologous radioligand was employed. The first of these strategies was adopted for the routine assay. Specificity relative to hydroxylated metabolites was a function both of antiserum selectivity and sample preparation. High plasma concentrations of drugs concomitantly administered to epileptics posed special analytical problems. Assay sensitivity is 40 pg/ml in plasma and the interassay CV is about 5%.

Cross Reactions↗

PubMed1989

The noncompetitive N-methyl-D-aspartate receptor antagonist, MK-801 profoundly reduces volatile anesthetic requirements in rabbits.

Rabbits anesthetized with volatile anesthetics were given bolus doses of the n-methyl-D-aspartate (NMDA) receptor antagonist MK-801. Following observation and recording of the hemodynamic and electroencephalographic effects of MK-801, the animals were tested for requirements of volatile anesthetic to prevent movement to a noxious stimulus. It was demonstrated that MK-801 significantly reduced anesthetic requirements in a dose-dependent manner, while also affecting hemodynamics and the electroencephalogram in a manner consistent with the production of a deeper plane of anesthesia.

Anesthesia↗

PubMed1989

Effect of excitatory amino acid receptor blocker MK-801 on overall, neurologic, and morphologic outcome after prolonged cardiac arrest in dogs.

Excitatory amino acids accumulating in the brain during ischemia may cause selective neuronal damage postischemia. This hypothesis was tested in a series of studies using MK-801, an N-methyl-D-aspartate (NMDA) receptor blocker, in a reproducible outcome model of prolonged cardiac arrest in dogs. After normothermic ventricular fibrillation cardiac arrest, the dogs were resuscitated with closed-chest femoral veno-arterial cardiopulmonary bypass. At 4 h they were separated from bypass, ventilation was controlled for 20 h, and intensive care was continued to 96 h. In Study I, ventricular fibrilation cardiac arrest (no-flow) was 17 min; starting immediately with reperfusion, MK-801 1200 mg/kg (n = 5) or an equal volume of placebo (n = 5) was infused over 12 h in blinded, randomized fashion. In Study II, the duration of the no-flow period was reduced to 15 min, and MK-801 2400 mg.kg-1 (n = 4) or placebo (n = 4) was infused. In Study III, no-flow lasted for 15 min, and MK-801 2400 mg/kg was started 30 min before ventricular fibrillation (n = 4); comparison was with Study II controls. In all three studies, MK-801 plasma concentrations peaked at greater than 50 ng/ml and were 15-30 ng/ml over 12 h. All 22 dogs of experiments within protocol survived with severe brain damage. MK-801 delayed return of pupillary reactivity, EEG activity, consciousness, and respiration, necessitating longer periods of controlled ventilation. Neurologic deficit scores, overall performance categories, and brain and heart morphologic damage scores at 96 h did not differ between placebo and MK-801 pretreatment or post-treatment groups. These negative outcome results after prolonged cardiac arrest do not negate the hyperexcitability hypothesis of selective vulnerability, but suggest the existance of additional mechanisms of secondary brain damage.

Animals↗

PubMed1988

Purification and composition of a novel gastrointestinal tumor-associated glycoprotein expressing sialylated lacto-N-fucopentaose II (CA 19-9).

Monoclonal antibody 1116NS 19-9 (Mab 19-9) exhibits selective reactivity with human gastrointestinal carcinomas and recognizes a carbohydrate determinant (CA 19-9) defined as a sialylated lacto-N-fucopentaose II. A scheme was devised for the purification of a human gastrointestinal tumor-associated glycoprotein antigen expressing CA 19-9 from colorectal carcinoma cell line SW1116 culture media in high yield. The key steps in the purification were immunoaffinity column chromatography with Mab 19-9 followed by reduction and alkylation of the specifically bound proteins in the presence of 6 M guanidine hydrochloride and a second Mab 19-9 immunoaffinity fractionation. The purified CA 19-9 containing glycoprotein ran as a single band on sodium dodecyl sulfate-polyacrylamide gradient gels with an apparent molecular mass of 210 kilodaltons. In the absence of detergents, this purified glycoprotein apparently reassociated to form aggregates of 600-2000 kilodaltons molecular mass as determined by size-exclusion chromatography. Amino acid analysis of CA 19-9 containing glycoprotein revealed that serine, threonine, and proline together accounted for greater than 35% of the amino acid residues, consistent with a mucin-like structure for the protein. Carbohydrate compositional analysis, however, was in contrast to a typical mucin with a fucose:mannose:galactose:N-acetylgalactosamine: N-acetylglucosamine:N-acetylneuraminic acid molar ratio of 4:1:12:2.5:5:5. The presence of both N-acetylgalactosamine and mannose suggested that both O- and N-linked oligosaccharides may exist on CA 19-9 containing glycoprotein. Protein and carbohydrate analyses indicated that this novel tumor-associated glycoprotein was 85% carbohydrate by weight. This purification procedure may be applicable to the isolation of other epithelial tumor-associated antigens.

Amino Acids↗

PubMed1984

Monitoring human ovarian carcinoma with a combination of CA 125, CA 19-9, and carcinoembryonic antigen.

CA 125 and CA 19-9 are antigenic determinants associated with human epithelial ovarian carcinomas. Murine monoclonal antibodies have been raised against these determinants, and immunoradiometric assays have been developed to monitor antigen levels in the serum of cancer patients. This study was undertaken to determine whether concomitant measurement of CA 125, CA 19-9, and carcinoembryonic antigen would provide a more precise correlation with tumor progression or regression than could be obtained with any single assay. Among 105 patients with surgically demonstrable epithelial ovarian carcinoma, serum CA 125 levels were elevated (greater than 35 U/ml) in 83%, CA 19-9, levels (greater than 37 U/ml) in 17%, and carcinoembryonic antigen levels (greater than or equal to 2.5 ng/ml) in 37%. Within individual samples, no correlation was found among values for the three markers, but patients with elevated CA 19-9 levels also had increased levels of CA 125. At least one of the three markers was elevated in 90% of the subjects. When 41 patients were monitored serially over 2 to 60 months, alterations in CA 125 levels correlated with disease progression or regression in 94% of instances, whereas alterations in CA 19-9 levels correlated in 33% and alterations in carcinoembryonic antigen levels in 25% of instances. Concomitant measurement of CA 125, CA 19-9, and carcinoembryonic antigen did not prove superior to measurement of CA 125 alone in the monitoring of patients with epithelial ovarian carcinoma.

Adenocarcinoma↗

PubMed1983

Isolation, chemical composition, and molecular size of extracellular type II and type Ia polysaccharides of group B streptococci.

Polysaccharides carrying the type II- and type Ia-specific determinants of Lancefield group B streptococci were isolated and purified by anion-exchange chromatography and gel filtration from the supernatant culture medium after growth of strain 18RS21/67/1 (type II) and strain DS/1204/78 (type Ia), respectively. The average molecular weights of these polysaccharides were 97,000 (type II) and 94,000 (type Ia), as determined by reducing end group analyses. These molecular weights were in reasonably good agreement with molecular weights determined by gel filtration at high ionic strength on calibrated columns. The polysaccharides did not cross-react with antisera specific for the other type-specific determinants or with group B-specific antisera. Their content of galactose, glucose, glucosamine, and neuraminic acid (the last two calculated as N-acetyl derivatives) accounted for over 96% of their dry weight. The two polysaccharides differed from each other (and from type III polysaccharide) in their relative content of these monosaccharides. The molar ratios of galactose, glucose, and neuraminic acid to glucosamine were 3.3:2.3:1.35:1.0 for the type II polysaccharide and 2.0:0.8:1.4:1.0 for the type Ia polysaccharides. The results obtained indicate that these extracellular type II and Ia polysaccharides contain larger amounts of neuraminic acid than can be accounted for by previously proposed structures of their repeating units.

Antigens, Bacterial↗

PubMed1980

Soluble group- and type-specific antigens from type III group B Streptococcus.

Two soluble polysaccharide antigens of a type III group B Streptoccus were isolated from the culture medium after growth of strain M732 in a chemically defined broth supplemented with acid-hydrolyzed casein. The type- and group- specific antigens were isolated from the culture supernatant by anion-exchange chromatography with diethylaminoethyl-Sephacel. Two carbohydrate-containing peaks, which had serological reactivity with group B or type III antiserum, respectively, were eluted with a linear NaCl gradient and further purified by gel filtration. The type III polysaccharide was found to contain glucose, galactose, glucosamine, and sialic acid, whereas the group B polysaccharide contained galactose, glucosamine, and rhamnose. For the type III polysaccharide, sialic acid was shown to be the major immunodeterminant, and for the group B polysaccharide, rhamnose was the immunodominant sugar. Both the type III and group B polysaccharides were obtained in high yields without employing harsh physical or chemical treatment and both were immunologically distinct. By immunoelectrophoresis or counterimmunoelectrophoresis, type III antigen failed to react with group-specific antiserum and the group B antigen failed to react with type III antiserum.

Antigen-Antibody Reactions↗