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Biomedical subjects

W Sadée

Publications and source records attributed to W Sadée.

At least 127 records · Page 7Linked to original sources
PubMed1980

Analysis of purine ribonucleotides and deoxyribonucleotides in cell extracts by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) assay for the fourteen major cellular purine ribonucleotides and 2'-deoxyribonucleotides is presented. Following an initial separation by anion-exchange HPLC, the nucleotides are hydrolyzed to their respective nucleosides by alkaline phosphatase and quantified by reversed-phase HPLC and UV absorbance detection. The assay is reproducible, specific, and has a detection limit of 10 pmol/sample. The recovery of nucleosides derived from nucleotides is 85%. Purine nucleotide pool sizes have been measured in cultured mouse T lymphoma (S-49) cells before and after treatment with 2.0 microM mycophenolic acid, an inhibitor of the enzyme IMP dehydrogenase, for 3 h. Control nucleotide levels obtained by this method are consistent with those reported for S-49 cells using other methods, and the observed decrease in guanine nucleotides and increase in IMP after treatment with mycophenolic acid agree with previous reports.

Animals↗
PubMed1980

Opiate antagonist receptor binding in vivo: evidence for a new receptor binding model.

The in vivo accumulation and retention of the opiate antagonist tracers [3H]diprenorphine and [3H]naloxone at cerebral opiate receptor sites in rats exceed that expected from their known in vitro receptor affinities. The [3H]diprenorphine serum and brain levels can be stimulated with a pharmacokinetic model that contains the receptors in a micro-compartment. The receptor micro-compartment consists of a population of binding sites next to a diffusion boundary which restricts ligand diffusion away from the receptor. Such an arrangement introduces a delay in the binding equilibrium of potent antagonists with the receptor sites and an increase in the apparent in vivo receptor affinity at subsaturating doses of the ligand; at saturating ligand concentrations these functions of the receptor micro-compartment are abolished. A physiological interpretation of the receptor micro-compartment could be the location of clustered opiate receptor sites on the exterior cell surface next to the synaptic cleft as the diffusion boundary. This kinetic approach involving a combination of pharmacokinetics and drug-receptor interactions permits the quantitative analysis of receptor site availability in the intact animal. Our results support the hypothesis that only one receptor population affects the in vivo disposition of the antagonist tracers, while they do not exclude the presence of low affinity binding sites that have been observed with the use of [3H]naloxone in vitro. Moreover, the binding site population observed in vivo may be responsible for mediating opiate agonist analgesia.

Animals↗
PubMed1980

Antineoplastic agents: high-dose methotrexate and citrovorum factor rescue.

Therapeutic drug monitoring procedures after moderate and high-dose methotrexate (MTX) therapy are reviewed. Serum levels of MTX along with creatinine clearance and weight loss can serve to identify patients at risk of serious hematological toxicity. Preventive measures to avert or reduce MTX toxicity include increased citrovorum factor rescue treatment, hydration, and alkalinization of the urine in order to increase the urinary clearance of MTX and prevent its precipitation in acidic urine. The toxicity of MTX is associated with a prolonged retention of the drug in the body. Since the initial clearance of MTX correlates well with endogenous creatinine clearance, only patients with normal renal functions are eligible for high-dose MTX therapy; however, MTX-induced renal toxicity may impair renal function during the course of therapy. Therefore, careful drug monitoring techniques are essential and have contributed to the effective use of high-dose MTX, although the potential of serious toxicity cannot be completely prevented. Further studies are needed to understand the complex mechanisms by which MTX exerts its toxic and therapeutic effects in cancer patients.

Dose-Response Relationship, Drug↗
PubMed1980

Methotrexate and 7-hydroxymethotrexate: serum level monitoring by high-performance liquid chromatography.

We have developed a reverse-phase high-performance liquid chromatographic assay with ultraviolet detection at 303 nm for methotrexate (MTX) and 7-hydroxymethotrexate (7-OH-MTX) in serum, plasma, and cerebrospinal fluid. The procedure involves the concentration of MTX and 7-OH-MTX in the aqueous phase by an n-butanol-ether extraction, resulting in a sensitivity of 10-20 nM in serum. Serum levels of MTX correlated well with those obtained by a competitive dihydrofolate reductase binding assay (r = 0.989). The clinical utility of the assay was demonstrated by measuring MTX and 7-OH-MTX serum levels in 42 patient samples.

Chromatography, High Pressure Liquid↗
PubMed1979

Determination of uracil and thymine and their nucleosides and nucleotides in picomole amounts by gas chromatography mass spectrometry selected ion monitoring.

A stable isotope dilution method is presented by which uracil (Ura) and thymine (Thy) can be determined with high precision and sensitivity at the picomole level utilizing stable isotope dilution and gas chromatography electron impact mass spectrometry in the selected ion monitoring mode. [15N2]Ura and [2H3]Thy served as internal standards. The molecular ions as well as the [M-CH3]+ ion fragments of silylated Ura and Thy (Ura-TMS and Thy-TMS) were suitable for the assay which provides evidence of specificity, if identical results are obtained at both ions. Nucleosides and nucleotides of Ura and Thy were determined following quantitative hydrolysis in 6 N HCl at 180 degrees C for two hours. Other hydrolysis procedures did not give satisfactory results. Levels of free Ura and Thy were measured in human and rat plasma after solvent extraction with a sensitivity of 20-40 pm ml-1 demonstrating ready applicability of the assay method to biological samples. The potential physiological role of circulating Ura and Thy is discussed.

Animals↗
PubMed1979

Spironolactone-associated digoxin radioimmunoassay interference.

Apparent digoxin was measured in the serum of 21 patients receiving spironolactone and in 21 controls, by use of a sequential-saturation 3H-radioimmunoassay (RIA) and an equilibrium 125I-RIA. No patient had been given digoxin for at least four weeks. "Digoxin" values in the former group were significantly (p less than 0.05) higher than in the control group, and often were in or near the "therapeutic" range by the equilibrium 125I-RIA, but not by the sequential-saturation 3H-RIA. Canrenone (a major active metabolite of spironolactone) in the serum of the former group was measured by a newly developed liquid-chromatographic technique and correlated (r = 0.73) with "digoxin" concentrations by the 125I-RIA. However, external addition of canrenone to control serum in comparable concentrations did not cause appreciable "digoxin" values by the 125I-RIA. These findings suggest that other metabolites of spironolactone are responsible for the assay interference, the degree of which appears to depend on antibody specificity. Therefore, assay specificity should be established in clinical laboratories by using digoxin-free serum from patients ingesting spironolactone, and not by using spironolactone- or canrenone-fortified digoxin-free serum.

Digoxin↗
PubMed1979

Morphine persistence in rat brain and serum after single doses.

The disposition of morphine in rat brain and serum was determined over 48 hr after subcutaneous doses. Free morphine was measured by a specific assay using 3H-labeling together with high-pressure liquid chromatography separation, with a sensitivity of 1 nM (0.3 ng of morphine per ml). This study revealed the persistence of free morphine in nanomolar concentrations over at least 24 hr after a single analgesic dose. The terminal half-life of morphine elimination was 5 hours. Total radioactivity was retained in the body at much higher concentrations. Similar disposition of [C-1-3H]morphine and [N-14CH3] morphine ruled out any major metabolic alterations at these positions, including N-demethylation. Irreversible binding to insoluble tissue components, which has previously been linked to tolerance, was observed only to the extent of less than 20% of total tissue radioactivity and was not unique to brain tissue. The persistence of morphine and its metabolites may be related to protracted opiate effects such as withdrawal symptoms after addiction.

Animals↗
PubMed1978

The fluoropyrimidines: biochemical mechanisms and design of clinical trials.

Our understanding of the biochemical events of fluoropyrimidine-induced cytotoxicity remains incomplete. However, we have a good perception of the activation and degradation pathways of these agents. Additionally, from studies performed in vitro we are gaining a new appreciation of the interactions between methotrexate and the fluoropyrimidines. These studies suggest that the common clinical practice of simultaneously administering methotrexate and 5-fluorouracil may be disadvantageous. Several simple scheduling modifications of combination therapies with these two drugs could lead to improved clinical efficacy and deserve further investigation.

Antineoplastic Agents↗
PubMed1978

Hydroxylated metabolies of R,S-1-(tetrahydro-2-furanyl)-5-fluorouracil (Ftorafur) in rats and rabbits.

Two hydroxylated metabolies (M1 and M2) have been isolated from rabbit urine after administration of Ftorafur (FT). The structures of 3'-OH-FT and 4'-OH-FT were assigned to M1 and M2, respectively. A reverse-phase high performance liquid chromatography assay was developed for jeasuring FT, M1, M2, and 5-fluorouracil (FU) plasma levels. M1, M2, and FU were present in rabbit and rat plasma in greatly varying concentrations after FT administration. Pharmacokinetic studies suggest that FU formation proceeds via metabolic intermediate(s) and that the extent of FT activation is variable. A horse liver thymidine phosphorylase ,reparation capable of catalyzing the conversion of beta-ribo-2'-deoxy-5-fluorouracil to FU was inactive against FT and M1. However, 20% of M2 was converted to FU by this enzume, which suggests that the urinary metabolite M2 consisted of a mixture of enantiomers with 20% present in the natural beta-D configuration. The stereochemistry of M1 remains unknown. Hydroxylation of FT to beta-D-4'-OH-FT and subsequent cleavage to FU by thymidine phosphorylase represents one possible activation mechanism of FT to FU. ,owever, lack of correlation between plasma levels of M2 and FU indicates that this mode of metabolic activation may account for only part of the overall activation of FT in vivo.

Animals↗
PubMed1977

Tissue distribution of 3H-canrenoate potassium in rabbits.

Plasma and various organ concentrations of canrenone, canrenoate, and total 3H-activity were measured following single doses of 20 mg of 3H-canrenoate/kg iv to rabbits. Organs studied included heart, lungs, brain, kidneys, liver, adrenal glands, and spleen. Canrenoate was shown to be in rapid equilibrium with canrenone. Both were eliminated from plasma and other tissues with a half-life of about 1 hr. Plasma concentrations of both drugs were equal as early as 10 min after intravenous drug administration. Canrenone was concentrated about 10-fold in organ tissues when compared to plasma, while no such preferential uptake was found with canrenoate. Total 3H-activity declined slowly in all tissues with a half-life of approximately 15 hr, indicating extensive metabolism and metabolite retention in the rabbit.

Animals↗
PubMed1977

Synthesis of 5-azacytidine-6-13C and -6-14C.

5-Azacytidine (1) labeled with 13C or 14C at the chemically labile C-6 position was synthesized. A method utilizing hydrolytic opening of the triazine ring followed by recyclization with dimethylformamide dimethyl acetal was used. Urinary and biliary excretion was measured in rabbits following intravenous doses of 1-4-14C and 1-6-14C. Differences in recoveries of the dose from 4-14C and 6-14C demonstrate that ring cleavage of 1 with loss of the C-6 carbon represents a major metabolite route.

Animals↗
PubMed1977

Measurement of procainamide and N-acetylprocainamide in serum by high-performance liquid chromatography.

We measured procainamide (I) and its metabolite, N-acetylprocainamide (II), in human serum samples by solvent extraction, high-performance liquid chromatography on a reverse phase column, and detection at 280 nm, with use of external standards. The method requires 0.2 ml of serum and is sensitive to 0.3 mg of I and 0.6 mg of II per liter of serum, with intra-assay standard deviations of 0.22 and 0.24 mg/liter, respectively, at 5 mg/liter (N=10) and inter-assay standard deviations of 0.63 and 0.81 mg/liter, respectively, at 7.5 mg/liter (CV 8.4 and 10.5%, respectively, n = 20). Concentrations measured by high-performance liquid chromatography and by an established fluorescence technique correlated well (r = 0.98 for I and 0.97 for II). No interfering substances were found in 20 randomly selected sera from patients receiving a large number of other drugs. Of the pure drug substances tested only sulfathiazole interfered with the assay of II. The method is therefore suitable for routinely monitoring these compounds in serum in a clinical laboratory. The high concentrations of the metabolite in a significant number of patients demonstrate the need to consider it as well as the parent drug as guides in optimizing dosage regiments for I.

Chromatography, High Pressure Liquid↗