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PubMed1999

Examination of co-complexes for radiolabeling of platelets in positron emission tomographic studies.

Oxine, tropolonate, and mercaptopyridine-N-oxide (MPO) have been widely used with 111In for platelet labeling. The use of positron emission tomography (PET) radioisotopes for platelet labeling would offer a higher sensitivity and resolution over conventional imaging. The medium half-life PET radioisotope 55Co (t1/2 = 18.2 hours) would enable quantitative uptake and cell kinetic studies with radiolabeled platelets. To identify the optimal complex for radiolabeling of platelets with 55Co, we investigated the platelet uptake of 57Co-oxine, 57Co-tropolonate, and 57Co-MPO in varying different parameters. The platelet uptake of Co-complexes was generally low (5-12%), dependent on time and temperature of incubation and density of platelets but independent of the amount of radioactivity. These findings are not promising for potential PET application.

Adult↗
PubMed1999

Platelet labeling with 67Ga chelates.

68Ga-labeled platelets could be useful for positron emission tomographic (PET) studies. In order to identify the optimal chelate for radiolabeling of platelets with 68Ga, we investigated the platelet uptake of 67Ga-oxine, -tropolone and -MPO. The platelet uptake of 67Ga-oxine and -tropolone is very low (< 5%). The platelet uptake of 67Ga-MPO, in contrast, increases with platelet density (highest at 10(9) platelets/ml) up to 18%. Our data provide evidence that only 68Ga-MPO could be useful for PET-studies.

Adult↗
PubMed1989

Roles of colchicine rings B and C in the binding process to tubulin.

The interactions of tubulin with colchicine analogues in which the tropolone methyl ether ring had been transformed into a p-carbomethoxybenzene have been characterized. The analogues were allocolchicine (ALLO) and 2,3,4-trimethoxy-4'-carbomethoxy-1,1'-biphenyl (TCB), the first being transformed colchicine and the second transformed colchicine with ring B eliminated. The binding of both analogues has been shown to be specific for the colchicine binding site on tubulin by competition with colchicine and podophyllotoxin. Both analogues bind reversibly to tubulin with the generation of ligand fluorescence. The binding of ALLO is slow, the fluorescence reaching a steady state in the same time span as colchicine; that of TCB is rapid. The displacement of ALLO by podophyllotoxin proceeds with a half-life of ca. 40 min. Binding isotherms generated from gel filtration and fluorescence measurements have shown that both analogues bind to tubulin with a stoichiometry of 1 mol of analogue/mol of alpha-beta tubulin. The equilibrium binding constants at 25 degrees C have been found to be (9.2 +/- 2.5) x 10(5) M-1 for ALLO and (1.0 +/- 0.2) X 10(5) M-1 for TCB. Binding of both analogues was accompanied by quenching of protein fluorescence, perturbation of the far-ultraviolet circular dichroism of tubulin, and induction of the tubulin GTPase activity, similarly to colchicine binding. Both inhibited microtubule assembly in vitro, ALLO substoichiometrically, and both induced the abnormal cooperative polymerization of tubulin, which is characteristic of the tubulin-colchicine complex. Analysis in terms of the simple bifunctional ligand binding mechanism developed for colchicine [Andreu, J.M., & Timasheff, S.N. (1982) Biochemistry 21, 534-543] and comparison with the binding of the colchicine two-ring analogue, 2-methoxy-5-(2,3,4-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-one [Andreu, J. M., Gorbunoff, M. J., Lee, J. C., & Timasheff, S. N. (1984) Biochemistry 23, 1742-1752], have shown that transformation of the tropolone methyl ether part of colchicine into p-carbomethoxybenzene weakens the standard free energy of binding to tubulin by 1.4 +/- 0.1 kcal/mol, while elimination of ring B weakens it by 1.0 +/- 0.1 kcal/mol. The roles of rings C and B of colchicine in the thermodynamic and kinetic mechanisms of binding to tubulin were analyzed in terms of these findings.

Animals↗
PubMed2001

Partial purification, characterization, and histochemical localization of fully latent desert truffle (Terfezia claveryi Chatin) polyphenol oxidase.

In the present paper, a fully latent polyphenol oxidase (PPO) from desert truffle (Terfezia claveryi Chatin) ascocarps is described for the first time. The enzyme was partially purified by using phase partitioning in Triton X-114 (TX-114). The achieved purification was 2-fold from a crude extract, with a 66% recovery of activity. The interfering lipids were reduced to 13% of the original content. In addition, the purification gave rise to a reduction of phenolic compounds to only 37.5%, thus avoiding the postpurification tanning of the enzyme. Latent PPO was activated by the anionic surfactant sodium dodecyl sulfate (SDS) or by incubation with trypsin. The amount of SDS necessary to obtain a maximum activation was dependent on the nature of the substrate. The use of SDS also permitted the histochemical localization of the latent enzyme within the ascocarp. Terfezia polyphenol oxidase was kinetically characterized using two phenolic substrates (L-DOPA and tert-butylcatechol). The latter substrate presented inhibition at high substrate concentration with a K(si) of 6.3 mM. Different inhibiting agents (kojic and cinnamic acid, mimosine and tropolone) were also studied, tropolone being the most effective.

Ascomycota↗
PubMed1986

Enantiomers of 3-(3,4-dihydroxyphenyl)- and 3-(3-hydroxyphenyl)-N-n-propylpiperidine: central pre- and postsynaptic dopaminergic effects and pharmacokinetics.

This study emphasizes the importance of the metabolic conversion of the enantiomers of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP) into their catechol analogues, the enantiomers of 3-(3,4-dihydroxyphenyl)-N-n-propylpiperidine. These isomers are both shown to be excellent substrates for COMT, with a slight preference for the S-(-) enantiomer. Assessment of the dopaminergic activity of these catechols and the results from the determination of brain levels of the enantiomers of 3-PPP and their metabolites indicate that the metabolites probably do not alter the pharmacological profiles established for (R)-(+)- and (S)-(-)-3-PPP. The conversion of the monophenols into catecholic metabolites is only 1-5%, and the further conversion of these catecholic metabolites into methoxylated analogues is very rapid. However, the very interesting observation was made that, when inhibiting COMT by means of tropolone and subsequently treating the rats with high doses of (S)-(-)-3-PPP (ip), postsynaptic dopaminergic activity was elicited. This has never been seen for (S)-(-)-3-PPP without tropolone pretreatment and might indicate that, in this special case, the catecholic metabolite affects the in vivo pharmacological profile of (S)-(-)-3-PPP.

Animals↗
PubMed1996

Synthesis, physicochemical properties, and biological evaluation of hydroxypyranones and hydroxypyridinones: novel bidentate ligands for cell-labeling.

The synthesis of a range of hydroxypyranones and hydroxypyridinones with potential for the chelation of indium(III) is described. The crystal structures of two of the indium complexes are presented. The distribution coefficients of the ligands and the corresponding iron(III), gallium(III), and indium(III) complexes are reported. Good linear relationships between the distribution coefficients of the iron and gallium complexes and iron and indium complexes were obtained. In contrast a nonlinear relationship was obtained between the distribution coefficient of the free ligand and the distribution coefficient of the three groups of complexes. This latter relationship was used to identify compounds with optimal cell labeling properties. Two such compounds both 6-(alkoxymethyl)-3-hydroxy-4H-pyran-4-ones have been compared with tropolone for their ability to label human leucocytes with 111In. The leucocyte labeling efficiencies of the selected ligands were greater and the in-vitro plasma stabilities were similar to that of 111In-tropolonate. These results suggest that the new bidentate ligands may offer advantages over those currently used for cell-labeling.

Cells↗
PubMed2003

Species-specific isotope dilution analysis of mono-, di, and tri-butyltin compounds in sediment using gas chromatography-inductively coupled plasma mass spectrometry with synthesized 118Sn-enriched butyltins.

A species-specific isotope dilution (ID) method is described for the determination of mono-, di, and tri-butyltin compounds in sediment by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS), where the mixture of 118Sn-enriched butyltin compounds synthesized in our laboratory was used as a spike. A correction method for the mass bias, a quantitative extraction of the butyltins from sediment, and an assay for the concentration of the standard solution for the reverse ID procedure were investigated to achieve a reliable ID analysis. The spike solution was added with tri-propyltin (TPrT), and the butyltins were extracted by mechanical shaking into acetic acid-tropolone-toluene. The extracted butyltins were ethylated with sodium tetraethylborate and measured by GC-ICP-MS. The mass bias correction factor for the butyltins was calculated with the measured area ratio of 120Sn/118Sn of TPrT in each chromatographic run, and the correction was carried out. The mass bias was well corrected with this in-run correction (the standard uncertainties of the corrected 120Sn/118Sn for the butyltins were in the range 0.03-0.45%, typically 0.25%, with triplicate measurement corresponding to 0.02-0.37% mass bias). The extraction efficiency of mono-butyltin (MBT) from sediment was improved by using tropolone-toluene as the solvent. Well-defined standard solutions for the reverse-ID procedure could be obtained by an assay for the purities of the natural abundance butyltin chloride reagents used for preparing the standard solutions. Overall uncertainties associated with the present method were estimated, where the sediment certified reference materials, PACS-2 and BCR 646, were analyzed. The uncertainty arising from the extraction was the main contributor to the overall uncertainties for MBT and di-butyltin (DBT) determinations, while with the case of tri-butyltin (TBT) determination the uncertainties arising from the purity of TBT chloride reagent used for preparing the standard solution was a large contributor to the overall uncertainties although the uncertainty arising from the extraction was also a main contributor. The analytical results of MBT, DBT, and TBT in both reference materials, except for MBT results in PACS-2, were in good agreement with the certified values in each. The result of MBT in PACS-2 (0.677 +/- 0.049 microg g(-1) as tin, mean +/- expanded uncertainty) was significantly higher than the certified value (0.45 +/- 0.05 microg g(-1)), but closely matched with the lately reported values (Rajendran, Tao, Nakazato and Miyazaki, Analyst, 2000, 125, 1757: 0.62 +/- 0.02 microg g(-1); Chiron, Roy, Cottier and Jeannot, J. Chromatogr. A, 2000, 879, 137: 0.634 +/- 0.082 microg g(-1); Alonso, Encinar, Gonzalez and Sanz-Medal, Anal. Bioanal. Chem., 2002, 373, 432: 0.64 +/- 0.04 microg g(-1). The present method is concluded to be reliable for the determination of MBT, DBT, and TBT in sediment.

Journal Article↗
PubMed2004

Liquid chromatography-hydride generation-atomic absorption spectrometry for the speciation of tin in seafoods.

Liquid chromatography with hydride generation atomic absorption spectrometry as the detection system was applied to the separation and determination of inorganic tin, tributyltin, dibutyltin, monobutyltin, diphenyltin and monophenyltin. A reversed phase C18 column and a methanol/water/acetic acid (70:27:3, v/v/v) mixture containing 0.05%(v/v) triethylamine and 0.1%(w/v) tropolone as the mobile phase (isocratic elution) were used. Extraction of organotins from the samples was carried out using methanol containing 0.05%(w/v) tropolone, a process that was repeated twice. The supernatants were shaken with water and dichloromethane in a separating funnel and the organic phase was collected and evaporated to dryness. When the method was applied to the speciation of tin in fresh and canned mussels, no organotins above the detection limits were identified in any of the samples, inorganic tin being the only species detected. The reliability of the procedure was checked by analyzing the total tin content of the samples by electrothermal atomic absorption spectrometry and by speciation of tin in a certified reference material, mussel tissue (CRM 477). The method can be used for environmental monitoring of organotins contaminated samples.

Chromatography, Liquid↗
PubMed2004

Antiferromagnetic coupling between rare earth ions and semiquinones in a series of 1:1 complexes.

We use the strategy of diamagnetic substitution for obtaining information on the crystal field effects in paramagnetic rare earth ions using the homologous series of compounds with the diamagnetic tropolonato ligand, Ln(Trp)(HBPz(3))(2), and the paramagnetic semiquinone ligand, Ln(DTBSQ)(HBPz(3))(2), (DTBSQ = 3,5-di-tert-butylsemiquinonato, Trp = tropolonate, HBPz(3)= hydrotrispyrazolylborate) for Ln = Sm(iii), Eu(iii), Gd(iii), Tb(iii), Dy(iii), Ho(iii), Er(iii) or Yb(iii). The X-ray crystal structure of a new form of tropolonate derivative is presented, which shows, as expected, a marked similarity with the structure of the semiquinonate derivative. The Ln(Trp)(HBPz(3))(2) derivatives were then used as a reference for the qualitative determination of crystal field effects in the exchange coupled semiquinone derivatives. Through magnetisation and susceptibility measurements this empirical diamagnetic substitution method evidenced for Er(iii), Tb(iii), Dy(iii) and Yb(iii) derivatives a dominating antiferromagnetic coupling. The increased antiferromagnetic contribution compared to other radical-rare earth metal complexes formed by nitronyl nitroxide ligands may be related to the increased donor strength of the semiquinone ligand.

Journal Article↗
PubMed2005

Dynamical hydrogen atom tunneling in dichlorotropolone: a combined quantum, semiclassical, and classical study.

Based on the Cartesian Reaction Surface framework we construct a four-dimensional potential for the tropolone derivative 3,7-dichlorotropolone, a molecule with an intramolecular O-H...O hydrogen bond. The reduced configuration space involves the in-plane hydrogen atom coordinates, a symmetric O-O vibrational mode, and an antisymmetric mode related to deformations of the seven-membered ring. The system is characterized in terms of quantum mechanical computations of the low-lying eigenstates as well as a classical and semiclassical analysis of spectra obtained via Fourier transforming autocorrelation functions. For the semiclassical analysis we utilize the amplitude-free correlation function method [K. Hotta and K. Takatsuka, J. Phys. A 36, 4785 (2003)]. Our results demonstrate substantial anharmonic couplings leading to highly correlated wave functions even at moderate energies. Furthermore, the importance of dynamical tunneling in tropolone is suggested since many low-lying states--including the ground state--lie above the classical saddle point but nevertheless appear as split pairs.

Journal Article↗
PubMed1991

New possibilities in erythrocyte survival studies with the application of a Well-type germanium semiconductor detector.

The application of a Well-type germanium semiconductor detector creates new possibilities in erythrocyte survival studies. Using 51Cr, the effective dose equivalent in a standard procedure can be reduced from approximately 780 to 2 microSv. The properties of the detector, namely, high efficiency and high energy resolution, also enable the application of two or even more radionuclides within one individual. This is demonstrated by some experiments utilizing a novel dual-label technique with 57Co tropolonate and 58Co tropolonate. Although this new dual-label technique needs further investigation, it underlines the potential possibilities of studying certain unanswered but clinically relevant questions in the field of transfusion medicine with the application of a Well-type germanium semiconductor detector.

Adult↗
PubMed1987

Inhibition of catechol-O-methyltransferase by 6,7-dihydroxy-3,4-dihydroisoquinolines related to dopamine: demonstration using liquid chromatography and a novel substrate for O-methylation.

We report that 6,7-dihydroxy-3,4-dihydroisoquinolines related to dopamine are potent inhibitors of catechol-O-methyltransferase (COMT), but are not apparent substrates for the enzyme in vitro or in vivo. Three dihydroxy (catecholic) dihydroisoquinolines, including the 1-benzyl (DesDHP) and the 1-methyl (DSAL) analogs, were found to inhibit COMT activity in rat liver supernatant more effectively than the well-known inhibitor, tropolone. Inhibition of O-methylation was uncompetitive with substrate, and O-methylated products of the catecholic dihydroisoquinolines were undetectable. For these in vitro studies, a facile liquid chromatographic assay was developed utilizing as a site-specific substrate, 1-methyl-6,7-dihydroxy-tetrahydroisoquinoline-1-carboxylate (salsolinol-1-carboxylate). This catechol produces only one phenolic product isomer when incubated with liver supernatant and S-adenosylmethionine. Following central injection of DSAL in rats, inhibition of brain COMT in vivo was indicated by the reduced brain levels of homovanillic acid, but not of 3,4-dihydroxyphenylacetic acid. Furthermore, O-methylated DSAL metabolites could not be detected in brain by liquid or gas chromatography. We suggest that 6,7-dihydroxy-dihydroisoquinolines are "nonmethylatable" COMT inhibitors because they exist as quinoidal tautomers resembling pyridones or tropolones rather than as catechols. Quinoid formation is supported by the fluorescence and ultraviolet spectra for DSAL and its O-methyl derivatives. The experiments reveal a new class of COMT inhibitors that may be of pharmacological and mechanistic value. Additionally, 3,4-dihydroisoquinolines could arise endogenously via oxidation of the 1,2,3,4-tetrahydroisoquinolines which are ingested or produced from cellular catecholamine condensations. However, it is unlikely that dihydroisoquinoline (e.g., DSAL) concentrations necessary to inhibit COMT significantly would be attained via endogenous pathways.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1971

Drug-induced changes in the release of ( 3 H)-noradrenaline from field stimulated rat iris.

1. Isolated rat irides were incubated with [(3)H]-noradrenaline [(3)H-NA] (10(-7)M), superfused with buffer and then stimulated by an electrical field. The effect of desipramine, clonidine, phentolamine, phenoxybenzamine, GD131, normetanephrine and 4-tropolone-acetamide on the stimulation-induced overflow of [(3)H]-NA was tested by adding the drug to the superfusing buffer. The effect of pretreatment with phentolamine or phenoxybenzamine on the stimulation-induced overflow of [(3)H]-NA was also studied.2. The effect of desipramine, clonidine, phentolamine, phenoxybenzamine and GD131 on uptake of [(3)H]-NA in isolated irides was determined.3. Desipramine moderately increased the stimulation-induced overflow at concentrations which almost completely inhibited neuronal uptake. It was calculated that in the isolated rat iris 30-40% of the released [(3)H]-NA is inactivated by reuptake into the nerve terminal. This figure may represent the true reuptake percentage in this preparation. Desipramine-induced inhibition of [(3)H]-NA release from the nerve terminal, possibly via a negative feed-back mechanism, may also contribute to this low figure.4. Phentolamine and phenoxybenzamine, in concentrations or doses which did not inhibit neuronal uptake of [(3)H]-NA, consistently increased the stimulation-induced overflow. This increase was further augmented when neuronal uptake was inhibited.5. The alpha-adrenoceptor stimulating drug clonidine decreased the stimulation-induced overflow.6. GD131, normetanephrine and 4-tropolone-acetamide did not greatly affect the stimulation-induced overflow of [(3)H-NA].7. It is concluded that the increased [(3)H]-NA overflow obtained after alpha-adrenoceptor blockade is due to an increased [(3)H]-NA release from the nerve terminals.

Acetamides↗
PubMed1987

Variation in iron accumulation, transferrin membrane binding and DNA synthesis in the K-562 and U-937 cell lines induced by chelators and their iron complexes.

Eight chelators - 8-hydroxyquinoline, 1-hydroxypyridine-2-thione (omadine), tropolone, pyridoxal isonicotinoyl hydrazone, 2-methyl-3-hydroxypyr-4-one (maltol), 1-methyl-3-hydroxypyrid-2-one, 1,2-dimethyl-3-hydroxypyrid-4-one and mimosine--and their iron complexes were tested on cells of the established human tumour cell lines K-562 (erythroleukaemic) and U-937 (monoblastoid) for their effects on a) cellular accumulation of iron provided by transferrin (Tf) via receptor-mediated endocytosis, b) specific cell surface binding of Tf, c) cell viability and, d) DNA synthesis. The lipophilic chelators suppressed the accumulation of Tf-supplied iron in the K-562 cells and less so in the U-937 cells, whereas the effects of the other chelators were closer to control range. The lipophilic chelators pyridoxal isonicotinoyl hydrazone, tropolone, 8-hydroxyquinoline and omadine were found to be cytotoxic in this order, with the U-937 being generally more sensitive than K-562. The presence of iron diminished the toxicity. The DNA synthesis was also affected, from a partial suppression in K-562 to a slight increase in U-937 in the presence of pyridoxal isonicotinoyl hydrazone and to strong suppression with 8-hydroxyquinoline and omadine. Addition of iron partially reversed the inhibition. The other chelators had low cytotoxic effects that disappeared upon iron saturation. Maltol, particularly in the absence of iron, 1,2-dimethyl-3-hydroxypyrid-4-one and 1-methyl-3-hydroxypyrid-2-one supported DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA↗
PubMed1985

Ketamine: evidence of tissue specific inhibition of neuronal and extraneuronal catecholamine uptake processes.

Ketamine (1.1 X 10(-5) to 3.7 X 10(-4) M) potentiated catecholamine responses of rat anococcygeus muscle and rabbit aorta in vitro. In the anococcygeus, potentiation was abolished by cocaine (2.9 X 10(-5) M) pretreatment or by chemical sympathectomy using 6-hydroxydopamine (6-OHDA), but was unaffected by pretreatment with the extraneuronal uptake inhibitor cortisol (8.3 X 10(-5) M), or the catechol-O-methyltransferase inhibitor tropolone (2.4 X 10(-4) M). The action of ketamine mimicked the potentiating effect of cocaine on tyramine responses. In contrast, the potentiation by ketamine in rabbit aorta was unaffected by cocaine or 6-OHDA but was abolished by cortisol or tropolone; and ketamine potentiated tyramine responses, whereas cocaine inhibited them. Thus the mechanism of action by which ketamine produces potentiation of catecholamines in these two tissues is completely different. These results suggest that ketamine has the unusual ability to block neuronal and extraneuronal uptake and that the predominating mechanism will depend on the type of tissue examined and the morphology of its adrenergic innervation.

Animals↗
PubMed1988

Quantitation of acute experimental ocular inflammation with 111indium-leukocytes.

The cellular component of an acute ocular inflammation in rabbits was measured with autologous leukocytes exogenously labeled with 111Indium tropolonate. Inflammation was induced by intravitreal bacterial lipopolysaccharide (LPS). After 16 hr blood was removed, leukocytes separated, labeled with 111Indium tropolonate and reinjected. Three cell fractions were examined: a leukocyte rich fraction which had been prepared with Dextran; and polymorphonuclear and mononuclear leukocyte fractions which had been prepared using a discontinuous Percoll gradient. Two hours after labeled leukocytes were injected, measurements of 111Indium were made in blood, plasma, the whole eye and in ocular compartments. From these data the numbers of each leukocyte population present were estimated and compared directly to histopathologic changes. Both polymorphonuclear and mononuclear leukocytes entered ocular tissues during the 2 hr period beginning 20 hr after LPS injection. Altered ocular vascular permeability was successfully measured with 125Iodine-albumin in some of these same rabbits. Both the number and type of inflammatory cell entering ocular tissues during a set period of time of the inflammatory response could thus be measured. This technique provides an opportunity to define the relationship of leukocyte infiltration and altered ocular vascular permeability in ocular tissues during the inflammatory response.

Acute Disease↗
PubMed1978

The development of new iron-chelating drugs. II.

For the past several years, we have searched for an orally effective iron-chelating drug and report here on several compounds which warrant further investigations based on their ability to promote iron excretion in the hypertransfused rat. Administrered orally, 2,3-dihydroxybenzyolglycine induced both urinary and fecal iron excretion, suggesting that a conjugate of 2,3-dihydroxybenzoic acid may be more efficacious than the parent compound. Tropolone, although rather toxic, stimulated fecal excretion of iron when given p.o. at low doses. Evaluation of less toxic derivatives of tropolone appears to be justifiable. L-Histidine may also be of use in chelatin therapy. Fecal iron excretion is significantly increased in response to oral doses of this essential amino acid. Lastly, cholylhydroxamic acid proved to be the most efficacious oral agent examined thus far. A marked increase in fecal iron excretion results from its administration.

Animals↗
PubMed1987

Should platelets be radiolabelled in plasma medium?

Because of the low labelling efficiency of platelets with In-111 oxine in plasma containing media, most investigators have labelled platelets in plasma-free media. However, labelling of platelets with In-111 oxine in plasma-free media may result in either: irreversible damage leading to rapid clearance from the circulation and permanent hepatic sequestration; or reversible damage with transient hepatic sequestration without affecting the in vivo survival. Since human platelets can be labelled with In-111 oxine in plasma in sufficient efficiency for routine clinical use, they should be labelled in plasma whenever possible. The use of newer In-111 chelates, tropolone and mercaptopyridine-N-oxide, which label platelets with high efficiency in plasma as well as in plasma-free media, may offer another alternative.

Animals↗