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PubMed1988

[125I-BH-8-MeO-N-PAT, a new ligand for the study of 5-HT1A receptors in the central nervous system].

Specific radioactive ligands are needed for studying the pharmacological properties and the regional distribution of the different classes of 5-HT1 receptors within the central nervous system. We describe here the synthesis and some characteristics of the first iodinated specific ligand of 5-HT1A receptors. Like its parent compound, the agonist 8-hydroxy-2-(di-n-propylamino)tetralin or 8-OH-DPAT, [125I]-BH-8-MeO-N-PAT, exhibits a high affinity and excellent selectivity for 5-HT1A sites. Its high specific radioactivity makes this ligand a useful tool for studying 5-HT1A receptors in membranes and sections of the rat brain.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1984

125I-labeled crosslinking reagent that is hydrophilic, photoactivatable, and cleavable through an azo linkage.

A radioactive crosslinking reagent, N-[4-(p-azido-m-[125I]iodophenylazo)benzoyl]-3-aminopropyl-N' -oxysulfosuccinimide ester, has been synthesized. The reagent is photoactivatable, water-soluble, cleavable through an azo linkage, and labeled with 125I at the carrier-free specific activity of 2000 Ci/mmol. Any protein derivatized with the reagent is thus converted into an 125I-labeled photoaffinity probe. Crosslinks are formed following photolysis with 366-nm light, and cleavage by sodium dithionite results in the donation of radioactivity to the distal partner in crosslinked complexes. The newly labeled proteins are then analyzed by gel electrophoresis and autoradiography. The compound was prepared by iodination of N-[4-(p-aminophenylazo)benzoyl]-3-aminopropionic acid using carrier-free Na125I and chloramine-T, followed by azide formation and conversion to the water-soluble sulfosuccinimide ester. As a model system, protein A-Sepharose was derivatized with the reagent under subdued light. Each derivatized protein A molecule contained only one crosslinker. The derivatized protein A-Sepharose was then photolyzed in the presence of human serum and subsequently treated with sodium dithionite. Analysis of the serum by gel electrophoresis revealed that 1.1% of the radioactive label originally present on the protein A-Sepharose was transferred to the heavy chain of IgG, which was the most intensely labeled protein in the gel. The next most intensely labeled protein was IgG light chain, which incorporated radioactivity that was lower by a factor of 3.6 than that of the heavy chain. These results demonstrated the specificity of the derivatized protein A-Sepharose as a photoaffinity probe. Photolabeling of IgG was the result of nitrene-mediated reactions and was not due to the incorporation of free 125I.

Autoradiography↗
PubMed1996

Mitochondria act as a reservoir for the basic amine HIPDM in the lung.

The lungs are a site for the uptake, accumulation, and storage of exogenous basic amines. The compound N-N-N'-trimethyl-N'-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3 propanediamine (HIPDM) is a basic amine that can be labelled with radioactive iodine and detected by external counting. Intravenously injected 123I-HIPDM is extracted by the human lung, where it is retained in a slowly effluxable pool. In the present study, we measured HIPDM lung kinetics and subcellular distribution in rabbits given i.v. 125I-HIPDM. Rabbits were killed from 2 min to 5 h after injection, and the radioactivity retained in their lungs was measured. Subcellular lung fractions (nuclear, mitochondrial, lysosomal, microsomal and postmicrosomal supernatant) were assayed for HIPDM radioactivity, protein content, and distribution of specific marker enzymes. HIPDM lung clearance in rabbits was nearly identical to that of humans. Virtually all the HIPDM radioactivity in lungs (98+/-1%) was associated with subcellular membranous structures. The highest HIPDM specific radioactivity was found in the mitochondrial fraction, and the subcellular distribution profile closely resembled that of the mitochondrial marker enzyme succinate cytochrome c reductase. No redistribution of HIPDM among subcellular compartments was observed over a 5 h period after injection. The data indicate that mitochondria act as reservoir for HIPDM in the lungs and contribute to the pulmonary persistence of this compound. HIPDM can be used to investigate the pulmonary uptake of basic amines in health and in lung disease.

Animals↗
PubMed1992

[The significance of modifying factors in evaluating the effect of radionuclides].

The authors provide the data obtained in experimental animals, pertaining to the influence of certain modifying factors on metabolism and biological effects induced by radioactive isotopes of iodine, by transuranium elements and beryllium. Out of all the modifying factors investigated, the form of the introduced compound and age turned out the most significant ones.

Aging↗
PubMed1995

Technetium-99, iodine-129 and tritium in the waters of the Savannah River Site.

Surface water samples were collected from streams on and around the Savannah River Site (SRS) to assess current 3H, 99Tc, and 129I concentrations in the water. The SRS is a nuclear facility operated by Westinghouse Savannah River Company for the US Department of Energy. Water quality parameters were measured at the time of collection using field portable instrumentation. The tritium activity was determined by liquid scintillation spectrometry. The isotopes, 99Tc and 129I, were determined by isotope dilution/inductively coupled plasma-mass spectrometry (D.M. Beals, Determination of technetium-99 in aqueous samples by isotope dilution inductively coupled plasma-mass spectrometry. Presented at the 3rd International Conference on Nuclear and Radiochemistry, Vienna, September 1992, unpublished data; D.M. Beals, P. Chastagner and P.K. Turner, Analysis of iodine-129 in aqueous samples by inductively coupled plasma-mass spectrometry. Presented at the 38th Annual Conference on Bioassay, Analytical and Environmental Radiochemistry, Santa Fe, NM, November 1992). Elevated activities of 3H, 99Tc, and 129I were found in some surface streams of the SRS, principally due to migration of ground water from beneath old seepage basins, however the levels in the waters leaving the SRS are well below any regulatory guidelines.

Fresh Water↗
PubMed1996

Radiotracer binding to brain microsomes determined by thin-layer chromatography.

A thin-layer chromatography (TLC) assay was developed to monitor the interaction of radiotracers with brain microsomes. Murine brain microsomes were coated onto a zone of a TLC strip, the unreacted sites blocked with gelatin, and the radiotracers chromatographed over the microsomes. Radiotracers bound to the microsomes and were separated from the unreacted materials which migrated at or near the solvent front. Up to 80% of the applied radioactivity bound to the brain microsomes when using 99mTc-(d,l) hexamethyl-propyleneamine oxime (HMPAO) and 123I-(S)-2-hydroxy-3-iodo-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl) methyl]-benzamide (123I-IBZM) as tracers. On the other hand, the presumptive negative control materials p-I-15-phenyl-pentadecanoic acid-123I (123I-IPPA) and 99mTc-mercapto-acetyl triglycine (MAG3) bound poorly (7% and 4%, respectively). 99mTc-ethyl cysteinate dimer (ECD) interacted poorly (9.9%), a result thought to be consistent with its known inability to be metabolized by nonprimate brain tissue. Radiolabeled octreotide analogues (radiolabeled with 111In, I-131 or 99mTc) also bound, and the binding could be reduced by excess unlabeled octreotide. Also, chemical modification by acylation of Lys5 in 111In-labeled octreotide led to decreased binding (approximately 70%) compared to the original radiotracer. Chromatography of the various radiotracers over TLC strips coated only with gelatin was used to monitor nonspecific binding and was low and frequently below 5%. This technique does not require wash steps or centrifugation, and assays are rapidly completed. The assay could be useful in monitoring the interaction of radiotracers with brain microsomes and in evaluating and developing new radiotracers.

Animals↗
PubMed2003

Iodine-124 labelled annexin-V as a potential radiotracer to study apoptosis using positron emission tomography.

Annexin-V is a calcium-dependent protein that binds with high affinity to phosphaditylserine exposed during apoptosis. The aim of this study was to radiolabel annexin-V with iodine-124 for use as a potential probe of apoptosis by positron emission tomography. Annexin-V was radioiodinated directly using the cyclotron-produced positron emitter iodine-124 by the chloramine-T (CAT) method and indirectly by the pre-labelled reagent N-succinimidyl 3-[124I]iodobenzoate ([124I]m-SIB). Some reaction parameters of the CAT method such as reaction time and pH were optimised to give radiochemical yields of 22.3 +/- 2.6%(n = 3, gel-filtration). After incubation with [124I]m-SIB, radiolabelled annexin-V was obtained in 14% and 25% yield by FPLC and gel-filtration, respectively. The radiochemical purities from direct and indirect labelling were 97.7 +/- 1.0%(n = 3) and 96.7 +/- 2.1%(n = 3), respectively. The new radiotracers could be stored for up to four days without significant de-iodination. The biological activity of radiolabelled annexin-V was tested in control and camptothecin-treated (i.e. apoptotic) human leukaemic HL60 cells. A significantly higher (21%) binding in treated cells was observed with [125I]m-SIB-annexin-V. The binding of [125I]m-SIB labelled annexin-V to camptothecin treated cells was blocked (68%) by a 100-fold excess of unlabelled annexin-V.

Annexin A5↗
PubMed1990

[The contribution of single-photon emission-computed tomography in cerebral function diagnosis].

Single photon emission computed tomography (SPECT) makes it possible to visualize physiological and chemical processes in the cerebrum. In this technique, single photon emitting nuclides such as 99m technetium and 123 iodine, which are tagged to other compounds, or 133xenon, are used for the study of several clinical conditions. After injection of the radiopharmaceutic agent the radioactivity is measured by a rotating gamma-camera from numerous directions. Based on the measured values, its distribution within the brain can be computed and transformed in tomographic slices. We present our experience with the method in clinical practice using preferentially N-isopropyl-(123I)-p-iodoamphetamine (123I-IMP) and 99mTc hydroxymethyl-propylene-amine-oxime (99mTc-HMPAO). These substances are distributed in accordance with regional cerebral blood flow (rCBF). Hitherto, the application of the method has concentrated on the study of cerebrovascular disease and epilepsy. SPECT has contributed to a better understanding of the pathophysiological processes and their dynamics after ischemic infarction. The method also provides essential insights in epileptics. In partial epilepsy, a focus of reduced or enhanced tracer activity can be ascertained, dependent on the timing of the examination, in the interictal and ictal stage respectively. Even in the early course of senile dementia of Alzheimer type, zones of diminished neuronal activity in temporo-parietal and frontal cortex are demarcated. Preliminary results in psychiatric diseases and parkinsonism need further confirmation. In this connection future interest will focus especially upon the use of receptor ligands.

Brain↗
PubMed1993

A simplified method for quantitation of iodine-123 iodobenzamide in human plasma: a technical note.

To establish a quantitative single-photon emission tomography (SPET) procedure for imaging CNS D2 dopamine receptors, measurement of unchanged iodine-123 iodobenzamide (123I-IBZM) (a selective D2 ligand) in human plasma was investigated. There are three possible radioactive components in human plasma: hydrophilic compounds (iodide ion, etc.), lipophilic metabolites, and unchanged IBZM. Based on the difference in lipophilicity of IBZM and its lipophilic metabolites (LM), a new quantitative method of analysis of 123I-IBZM using a simple solvent extraction was developed. The selective extraction was achieved with n-octane/phosphate buffer (0.1 M, pH 7.4). Extraction efficiency was 93.2% +/- 0.3% (n = 15) for IBZM from plasma, while 99.3% +/- 0.2% (n = 12) of LM remained in the aqueous plasma fraction. Twenty-one confirmation tests with plasma containing known ratios of IBZM/LM, ranging between 0.39 and 7.60, were performed. The experimental results were very close to the values of the true ratios over the wide range (accuracy approximately 99%, relative standard error 6.6%). The data from this simplified method are comparable to those obtained by the high-performance liquid chromatography method. This improved method provides an easy and accurate way to quantify unchanged IBZM in human plasma. With appropriate kinetic modeling and in conjunction with a dedicated SPET imaging device for measuring quantitative information, it may be possible to develop a practical method for measuring D2 receptor density in vivo.

Benzamides↗
PubMed2001

Dose variance associated with calibration and administration of radiopharmaceuticals.

Variation in the amounts of radioactivity that is associated with dose calibration and administration of gamma-emitting radioactive drugs was studied. Health systems use radionuclide dose calibrators when they need to assay drugs for radioactivity. However, the radioactive drugs commonly used for therapeutic or diagnostic purposes are compounded and assayed in or administered from containers that differ from those containing the standard reference materials (SRMs). SRMs for four radionuclides--technetium 99m, indium 111, thallium 201, and iodine 131--were drawn up into vials and syringe-needle assemblies of volumes and sizes represented in clinical practice. In each sample, the amount of radioactivity was calculated and compared with values obtained from three dose calibrators. In addition, over a four-month period, 101 samples of technetium Tc 99m medronate injection with a desired activity of 20 mCi were prepared in syringes; the radioactive dose in each syringe was calibrated for administration to a patient at a specific time that day. The amounts of radioactivity at the time of preparation and the time of administration, the amount remaining in the syringe and needle after administration, and the amount reported as administered were recorded. Measurement with the dose calibrators of the SRMs in containers supplied by the National Institute of Standards and Technology showed radioactivity within 10% of the labeled amount, the percentage of variation regulations allow. Measurements of the SRMs in syringe-needle assemblies were within 10% for technetium 99m and thallium 201, 9-16% for iodine 131, and 15-26% for indium 111. The individual doses of technetium 99m medronate injection were, on average, administered on time, but doses were administered up to 75 minutes before and 107 minutes after the calibration time. The mean +/- S.D. amount administered was 19.0 +/- 1.34 mCi. The mean +/- S.D. amount reported administered was 20 +/- 0.24 mCi. How radiopharmaceuticals were dose calibrated and administered influenced the actual dose available to patients.

Calibration↗
PubMed1976

Iodinated versus fluorescent labelling in the radioallergosorbent test (RAST) for the determination of serum IgE levels.

Experiments were performed to determine the feasibility of replacing the radioactive 125I tag in the radioallergosorbent test (RAST) with a new fluorescent compound, 2-methoxy-2, 4-diphenyl-3 (2H)-furanone (MDPF). It was possible to discriminate a grass-allergic from a grass-non-allergic patient using the traditional RAST procedure with 125I-ant-IgE. However, when a fluorescent label, MDPF was attached to IgE using the same RAST procedure, it was not possible to discriminate between allergic and non-allergic responses. Additional experiments, using BSA and anti-BSA as a model, showed that it was possible to detect 0.025 ppm antigen using iodinated antiserum while the fluorescent tag had a lower limit of antigen detection of 0.20 ppm. It was possible to distinguish between allergic and non-allergic responses using 125I-N-succinimidyl-3(4-hydroxyphenyl) propionate (SHPP) which binds to protein in a manner similar to MDPF. These results suggested that the unsatisfactory fluorescence results were not due to an alteration of protein structure as a result of MDPF labelling. Although the fluorescence work was performed using a fluorimeter with optics and electronics optimized for detection of MDPF, sensitivity of the method was limited by high fluorescent background.

Allergens↗