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PubMed1984

Generation and characterization of radiolabeled diesel exhaust.

To evaluate the potential health risks associated with increased use of diesel engines, information is needed on the biological fate of inhaled diesel exhaust components. Appropriately radiolabeled exhaust produced by burning radiolabeled fuel could be used to gain this information. The purpose of this study was to characterize different radiolabeled diesel exhausts with respect to their potential use in studies of the biological fate of exhaust carbon particles and particle-associated organic compounds (particle extracts). A single-cylinder diesel engine was used to burn diesel fuel containing trace amounts of 14C-labeled hexadecane, dotriacontane, benzene, phenanthrene or benzo(a)pyrene. Greater than 98% of the 14C in all additives was converted to volatile materials upon combustion. The remainder was distributed in varying amounts between the carbon particles and particle extracts. Aromatic additives labeled carbon particles more efficiently than aliphatic additives. Column chromatography of the particle extracts showed that, in most cases, the majority of the radioactivity eluted in fractions identical to the specific fuel additive employed, suggesting that a large amount of the particle-associated organic compounds consisted of uncombusted fuel constituents. Applying an electrical load to the engine-electrical generator increased carbon particle radioactivity, but had variable effects on the amount of radioactivity in the particle extracts. 67Ga-tetramethylheptanedione was also studied as a fuel additive to label carbon particles. 67Ga was incorporated into the exhaust particles and lung deposition of particles in rats was found to be approximately 10%. However, the 67Ga-radiolabel was found to separate from the particles in vivo, making it an unsuitable radiolabel for studying the long-term lung retention of diesel exhaust carbonaceous particles.

Animals↗
PubMed1975

Biosynthesis of the polyoxins, nucleoside peptide antibiotics: glutamate as an origin of 2-amino-2-deoxy-L-xylonic acid (polyoxamic acid).

The biosynthetic origin of the carbon skeleton of 2-amino-2-deoxy-L-xylonic acid (polyoxamic acid) is described. This aminoaldonic acid is the N terminus of the nucleoside peptide antibiotics, the polyoxins, produced by Streptomyces cacaoi var. asoensis. In vivo experiments concerning incorporation and distribution of radioactivity from a number of 14C-labeled compounds have clearly shown that the carbon skeleton of glutamate is a precursor for this aminoaldonic acid and sugars are incorporated only after their conversion into gluamate through the glycolytic and the tricarboxylic acid cycle pathways. Experiments utilizing [14C]-acetate and succinate have also indicated multiple passages through the Krebs cycle are operating before their incorporation into polyoxamic acid via glutamate. The distribution of 14C between C-1 and C-5 of polyoxamic acid from [5-14C]glutamate experiment has indicated that 40% of glutamate incorporated only after the reversible conversion into alpha-ketoglutarate followed by the passage through the Krebs cycle. Lack of incorporation of 3H in the [1-14C;2-3H]- and [5-14C;2-3H]glutamate experiments is discussed in terms of a reaction(s) between glutamate and polyoxamic acid.

Acetates↗
PubMed2004

De novo biosynthesis and radiolabeling of mammalian digitalis-like factors.

BACKGROUND: Digoxin-like immunoreactive factors (DLIFs) are endogenous mammalian cardenolides with structural features similar to those of the plant-derived digitalis compounds. DLIFs and their structurally related forms (Dh-DLIFs) may serve as effectors of ion-transport activity mediated by their interaction with Na,K-ATPase and thus play a role as a new hormonal axis. Although some evidence implicates the adrenal gland as a tissue source for the DLIFs, little is known about the biosynthetic pathway producing these compounds. We now demonstrate de novo biosynthesis of DLIF by incorporation of radioactive carbon ((14)C) into the structures of both DLIF and Dh-DLIF. METHODS: We used a combination of reversed-phase HPLC techniques to separate the radioactive DLIF components after incorporation of (14)C into their structure by use of either [1,2-(14)C]acetic acid or [4-(14)C]cholesterol as precursors and a Y-1 mouse adrenocortical tumor cell line. We also stimulated and suppressed production of steroidogenesis by use of cAMP analogs and Mevastatin, respectively, to demonstrate the dependence of DLIF production on the cholesterol-dependent biosynthetic pathway. A combination of chromatographic mobility, immunoassays specific for digoxin and dihydrodigoxin, and deglycosylation using 5-sulfosalicylic acid were used to identify the DLIF and Dh-DLIF components. RESULTS: With cholesterol as precursor, the cells produced DLIF (7.5 mCi/mmol) with a labeling efficiency of 10%, whereas with acetate the cells produced DLIF (72.2 mCi/mmol) with a labeling efficiency of 0.08% of the total DLIF produced. The radiolabeled DLIF and Dh-DLIF molecules had identical chromatographic mobilities and stoichiometric removal of sugars as the previously characterized DLIFs isolated from different mammalian species and tissues. With radioactive cholesterol as precursor, the (14)C was incorporated into the DLIF-genin portion of the compounds and not the sugars. Interestingly, treatment of Y-1 cells with 8-bromoadenosine 3':5'-cAMP to stimulate steroidogenesis did not increase production of DLIF or Dh-DLIF but did increase production of progesterone. Mevastatin (5 micromol), an inhibitor of the enzyme hydroxymethylglutaryl-CoA reductase and thus of cholesterol biosynthesis, gave an 85% decrease in the production of (14)C-DLIF and progesterone, but only a modest 15% decrease in (14)C-Dh-DLIF production. CONCLUSIONS: These data demonstrate that the adrenal cell has the cellular machinery necessary for de novo biosynthesis of DLIF and Dh-DLIF starting from a simple carbon pool and also support the concept that cholesterol is a major precursor of the DLIF compounds. This cell culture model provides a source of radiolabeled DLIF compounds for future experimental work.

Acetic Acid↗
PubMed1983

Circulating prostacyclin metabolites in the dog.

The present study was designed to determine the concentration of prostacyclin (PGI2) metabolites in the blood of the dog. After a bolus i.v. dose of [11 beta-3H]PGI2 (5 micrograms/kg) into each of five dogs, blood samples were withdrawn at 0.33, 0.67, 1, 3, 5, 20, 30, 60 and 120 min postdrug administration. Plasma samples were extracted and the radioactive components were analyzed by two-dimensional thin-layer chromatography with autoradiofluorography and radio-high-performance liquid chromatography. The compounds were identified by comparing their mobility with synthetic standards; only parallel responses observed in both tests constituted positive identification. Seven metabolites were identified by these two techniques: 6-keto-prostaglandin (PG)F1 alpha; 6-keto-PGE1; 2,3-dinor-6-keto-PGF 1 alpha; 2,3-dinor-13,14-dihydro-6,15-diketo-20-carboxyl PGF 1 alpha; and 2,3,18,19-tetranor-13,14-dihydro-6,15-diketo-20-carboxyl PGF 1 alpha. Several additional compounds, both polar and nonpolar in nature, which did not co-chromatograph with any of our standards were also detected. Early samples consisted predominantly of 6-keto-PGF 1 alpha and other 20-carbon metabolites. By 30 min, the predominant metabolites were the 16- and 18-carbon dicarboxylic acids. By 60 min, 85% of the radioactivity was associated with two unidentified polar compounds. The evidence suggests that 6-keto-PGF 1 alpha probably reflects only the transient levels of freshly entering PGI2 in the circulation, whereas levels of the most polar metabolites (e.g., dihydro-diketo-carboxyl tetranor-PGF 2 alpha) may be a better measure of the overall PGI2 presence due to its longer half-life in circulation.

Animals↗
PubMed1978

Microbial transformation of 14C-labeled 2,4,6-trinitrotoluene in an activated-sludge system.

The fate of 14C-labeled 2,4,6-trinitrotoluene (TNT) in an activated-sludge system was investigated. No [14C]TNT could be detected in the contents of an aerated reactor after 3 to 5 days of incubation. No significant 14CO2 was formed, and the radioactivity was about equally divided between the floc and the supernatant. The radioactive carbon present in the microflora was mainly associated with the lipid and protein components, but the characteristic constituents of these compounds (e.g., fatty acids and amino acids) were not radioactive. The major part of the 14C present in the lipid and protein fractions was found in precipitates that formed in both fractions. The solubility properties and infrared spectra of these precipitates suggested that they are macromolecular structures of the polyamide type formed by the reaction of TNT biotransformation products with lipids, fatty acids, and protein constituents of the microbial flora. This hypothesis is further supported by the correspondence of the infrared spectrum of the lipid precipitate with that of a model compound synthesized from TNT transformation products and lipid precursors. The resistance of these macromolecules to further biodegradation was paralleled by the reported resistance to microbial attack of polyamides containing similar linkages.

Bacteria↗
PubMed2001

In vivo pharmacokinetics of pyribenzoxim in rats.

Pyribenzoxim, benzophenone O-[2,6-bis(4,6-dimethoxypyrimidin-2-yloxy)benzoyl]oxime, is a new post-emergence herbicide providing broad-spectrum weed control in rice fields. [14C]Pyribenzoxim was used to study the pharmacokinetics of the compound after oral administration of a dose of 1000 mg kg-1 to male Sprague-Dawley rats. The material balance ranged from 97.3 to 99.7% of the administered dose and urinary and fecal recovery accounted for 97.1%, with the majority of radioactivity recovered in feces (88.6%) by 168 h after treatment. Elimination as volatile products or as carbon dioxide was negligible. The following values were obtained for the compound in the blood: AUC0-168 h, 28,400 micrograms equiv hg-1; Tmax, 12 h; Cmax, 372 micrograms equiv g-1; half-life, 53 h. Radioactivity in tissue decreased from 96.1% of applied radiocarbon at 6 h to 0.4% at 168 h and the highest concentration of radioactivity among the tissues was observed in liver while the lowest residues were found in brain. The elimination half-lives of radioactivity from tissues was in the range of 7 to 77 h and Tmax values of 12, 24 and 12 h were observed for blood, liver and kidney, respectively. Except for that in the digestive tract, the tissue-to-blood ratio (TBR) was highest in the liver.

Administration, Oral↗
PubMed1984

In vivo studies of opiate receptors.

To study opiate receptors noninvasively in vivo using positron emission tomography, techniques for preferentially labeling opiate receptors in vivo can be used. The rate at which receptor-bound ligand clears from the brain in vivo can be predicted by measuring the equilibrium dissociation constant (KD) at 37 degrees C in the presence of 100 mM sodium chloride and 100 microM guanyl-5'-imidodiphosphate, the drug distribution coefficient, and the molecular weight. A suitable ligand for labeling opiate receptors in vivo is diprenorphine, which binds to mu, delta, and kappa receptors with approximately equal affinity in vitro. However, in vivo diprenorphine may bind predominantly to one opiate receptor subtype, possibly the mu receptor. To predict the affinity for binding to the opiate receptor, a Hansch correlation was determined between the 50% inhibitory concentration for a series of halogen-substituted fentanyl analogs and electronic, lipophilic, and steric parameters. Radiochemical methods for the synthesis of carbon-11-labeled diprenorphine and lofentanil are presented.

Brain↗
PubMed1984

In vivo and in vitro pharmacokinetics and fate of furaltadone in meat- and milk-producing animals.

The metabolism of furaltadone was examined by an in vitro hepatic study in cows and goats and an in vivo study in goats using 14C-labeled and unlabeled drug. The half-life of furaltadone was 13 min in the homogenates of caprine and bovine liver and 35 min in the in vivo study of the goat. Less than 2% of the parent drug was present in the urine of animals dosed either intravenously or intramammarily. No furaltadone was detected in the milk after 24 h. Overall, the parent compound was rapidly absorbed, distributed, and widely degraded in the lactating goat. The compound, labeled at the 2-formyl carbon of the furan ring, had a radioactivity recovery of 81% in the feces and urine. Of the total radioactivity, 99.4% infused into the udder had been absorbed after 72 h. Tissue distributions of radioactivity in decreasing order of abundance were: kidney, udder, liver, duodenum, muscular tissue, adipose tissue, and bile.

Animals↗
PubMed2003

Dioxouranium-carboxylate complexes. Formation and stability of acetate species at different ionic strengths in NaCl(aq).

The formation and stability of UO2(2+)-acetate complexes was studied potentiometrically, at T = 25 degrees C, at different ionic strength, 0 < I < or = 1 mol dm(-3), in aqueous NaCl solutions. Computer analysis allowed us to find the species UO2(ac)+, UO2(ac)2(0), UO2(ac)3- and UO2(ac)3(OH)2-. The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. A critical examination of the present results is given together with a comprehensive analysis of literature data.

Acetates↗
PubMed1991

Metabolic activation of halogenated hydrocarbons in the conjunctival epithelium and excretory ducts of the intraorbital lacrimal gland in mice.

Autoradiographic studies were performed to determine the localization of irreversibly bound radioactivity in the eyes and accessory structures of mice exposed to 14C-labelled organic solvents in vivo or in vitro. A selective localization of bound radioactivity was observed in the conjunctival epithelium of mice given i.v. injections of 1,2-dibromoethane, chloroform, carbon tetrachloride or bromobenzene. Similar results were observed after instillation of chloroform or carbon tetrachloride in the conjunctival sac and after incubation of eyelids with the labelled compounds in vitro. A high level of irreversibly bound radioactivity was also observed in the excretory ducts of the intraorbital lacrimal glands of mice exposed to 1,2-dibromoethane in vivo and in vitro. After incubation of 14C-labelled 1,2-dibromoethane or chloroform with homogenates prepared from rat conjunctiva, the presence of irreversibly protein-bound radioactivity was detected. The results indicate that the conjunctival epithelium can metabolically activate halogenated organic solvents into products that bind to the tissue. The significance of a metabolic activation of chemicals in the pathogenesis of chemically induced lesions in the conjunctiva merits further attention.

Animals↗
PubMed1991

A method of studying pharmacokinetics in man at picomolar drug concentrations.

1. We describe a new method that enables the tissue kinetics of picomolar concentrations of drugs to be measured in man. The method is based on the administration of a drug, labelled with a short-lived positron-emitting radioisotope, such as carbon-11 (t1/2 = 20.4 min, beta + = 99.8%) or fluorine-18 (t1/2 = 109.8 min, beta + = 96.9%), which is then detected in vivo by an array of 10 large uncollimated sodium iodide scintillation detectors, arranged as five opposing pairs, with each pair collecting data over one major organ or region of the body. 2. To illustrate the scope of the new method we report the results of administering [O-methyl-11C]-diprenorphine, an established radioligand for central opiate (mu, kappa, and delta) receptors and L-6-[18F]-fluoro-DOPA, a marker for dopaminergic neurons. 3. Only 2-10 muCi (74-370 kBq) of radioactivity are used and, as a consequence of the high specific activities with which carbon-11 and fluorine-18 labelled compounds can be prepared, the method requires less than a nanomole of drug to be administered. In many cases, this amount of drug might be considered low enough to avoid any adverse biological effect. Furthermore repeat studies are possible in many without delivering unacceptable radiation burdens. 4. The high sensitivity realised for both radioactivity and mass suggests a mean for determining the human biodistribution of a new drug at a very early stage in its development. This has potential benefit to drug discovery programmes and to ensuing drug therapies.

Blood-Brain Barrier↗
PubMed1995

Synthesis of fluoroacetate from fluoride, glycerol, and beta-hydroxypyruvate by Streptomyces cattleya.

Streptomyces cattleya produces fluoroacetate and 4-fluorothreonine from inorganic fluoride added to the culture broth. We have shown by 19F nuclear magnetic resonance (NMR) spectrometry that fluoroacetate is accumulated first in the culture broth and that accumulation of 4-fluorothreonine is next. To show precursors of the carbon skeleton of fluoroacetate, we carried out tracer experiments with various 14C- and 13C-labeled compounds. Radioactivity of [U-14C]glucose, [U-14C]glycerol, [U-14C]serine, and [U-14C]beta-hydroxypyruvate was incorporated into fluoroacetate to an extent of 0.2 to 0.4%, whereas [3-14C]pyruvate, [2,3-14C]succinate, and [U-14C]aspartate were less efficiently incorporated (0.04 to 0.08%). The addition of [2-13C]glycerol to the mycelium suspension of Streptomyces cattleya caused exclusive enrichment of the carboxyl carbon of fluoroacetate with 13C; about 40% of carboxyl carbon of fluoroacetate was labeled with 13C. We studied the radioactivity incorporation of [3-14C]-, [U-14C]-, and [1-14C]beta-hydroxypyruvates to show that C-2 and C-3 of beta-hydroxypyruvate are exclusively converted to the carbon skeleton of fluoroacetate. These results suggest that the carbon skeleton of fluoroacetate derives from C-1 and C-2 of glycerol through beta-hydroxypyruvate, whose hydroxyl group is eventually replaced by fluoride.

Carbon Isotopes↗
PubMed1977

Microenvironment of the binding site in the lac carrier protein.

Studies with a homologous series of (N-dansyl)aminoalkyl-1-thio-beta-D-galactopyranosides containing two to six methylene carbons bridging the galactosyl and dansyl ends of the molecules are described. The compounds were utilized in radioactive and nonradioactive form, and binding of each homologue to membrane vesicles isolated from Escherichia coli ML 308-225 was measured directly by flow dialysis in the presence of D-lactate. The results are compared with the D-lactate-induced fluorescence enhancement observed with each dansylgalactoside and with the ability of N-methylpicolinium perchlorate to quench the fluorescence of the bound homologues. The binding affinity of the lac carrier protein for the probes varies directly with the length of the alkyl linkage, and the same number of binding sites is observed with each homologue. In contrast, however, the increase in fluorescence observed upon binding varies dramatically as the alkyl chain is increased in length, with the fluorescence exhibiting maximal values at two and six methylene carbons and a minimum at four methylene carbons. Furthermore, quenching by N-methylpicolinium perchlorate exhibits an inverse relationship and maximum quenching is observed with the 4 carbon homologue. Possible reasons for this behavior are discussed.

Bacterial Proteins↗
PubMed1967

Atmospheric transfer of carbon-14: a problem in fungus translocation studies.

The carbon-14-labeled carbon dioxide that is released by respiration after glucose labeled with carbon-14 is applied to fungal mycelium can be reabsorbed in highly significant amounts by distant mycelium and agar media in the same petri dishes. Atmospheric transfer of carbon-14 must be considered when using labeled organic compounds to study translocation in fungi.

Air Pollution, Radioactive↗