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At least 289 records · Page 16Linked to original sources
PubMed2003

Established theory of radiation-induced decay is not generalizable to Bolton-Hunter labeled peptides.

Peptide hormones radiolabeled with 125I are widely used for the pharmacological characterization of cognate receptors. As a prerequisite for calculating ligand affinities from competition binding assays, and for estimating receptor densities from such studies, it is necessary to know the concentration of bioactive radioligand that is used in respective experiments. It has been demonstrated previously that radioiodinated peptides undergo decay catastrophe, i.e. disintegration of the radioactive label leads to the concomitant destruction of the carrier peptide. Here, we demonstrate that decay catastrophe does not apply to two peptide hormones that are iodinated by Bolton-Hunter conjugation: cholecystokinin octapeptide and glucagon-like peptide 2. The function of aged samples of these radioligands at corresponding recombinantly expressed receptors was assessed by measuring ligand-induced inositol phosphate production or generation of cyclic AMP, respectively. Both of the tested compounds, although predicted by decay catastrophe to contain little or subthreshold remaining bioactivity, stimulated an unexpectedly high level of receptor-mediated second messenger signaling. Quantitative comparison of observed functions with those of corresponding unlabeled peptides suggested that the bioactivity of each radioligand had been largely conserved despite the radioactive decay of the iodine label. Consistent with an apparent absence of decay catastrophe, we noted that the specific radioactivity, when determined immediately following peptide iodination, was close to the theoretical maximum but exponentially decreased over time. These findings raise the possibility that attachment of a Bolton-Hunter conjugate may shield labeled peptides from radiation-induced damage, a scenario that should be considered when performing radioligand binding experiments.

Animals↗
PubMed1990

Effect of gamma-butyrolactone on the retrograde axonal transport of neurotensin in dopaminergic neurones.

gamma-Butyrolactone is a drug known to inhibit the flow of electrical impulses in dopaminergic neurones and to prevent dopamine release in the striatum. In this study, we investigated the effects of this compound on the retrograde transport of neurotensin in the nigrostriatal dopaminergic pathway. The amount of radioactivity measured in the substantia nigra after injection of iodinated neurotensin into the striatum and the time course of its accumulation were not found to be modified in gamma-butyrolactone-treated rats. We therefore conclude that the retrograde axonal transport of neurotensin in the nigrostriatal pathway is not affected by reduced dopaminergic firing or by inhibition of the striatal release of dopamine.

4-Butyrolactone↗
PubMed1988

Human placental LHRH receptor: agonist and antagonist labeling produces differences in the size of the non-denatured, solubilized receptor.

Membranes of human term placenta were labeled with several photosensitive and non-photosensitive analogues of LHRH. In both groups agonistic and antagonistic peptide structures were tested. The photolabeling amino acid azidophenylalanine was placed either in positions 2, 6 or 7. All compounds were specifically displacing iodinated Buserelin from human placental membranes and from rat pituitary membranes. The iodinated photolabels were displaced by cold Buserelin, some compounds however had a high non-specific binding. Photolabeling experiments on human placental membranes with radioactive photolabels produced all a band at 58,000 daltons in SDS-gel electrophoresis. Solubilization with a non-denaturing detergent and gel filtration produced a major radioactivity peak which was attributed to the LHRH receptor. All labeling experiments with agonist labels produced Kav's indifferent from each other but significantly different from the Kav's of antagonist labeled membranes. This result was confirmed with similar experiments carried out with radioactive Buserelin and a radioactive antagonist under non-photolytic conditions. It is therefore concluded that the placental LHRH receptor contains an LHRH binding component of 58,000 daltons but that the native receptor is composed of several proteins. It is also concluded that agonist occupation of the receptor induces the association of a further component which might be involved in the transmembrane signalling system. The agonist labeled, solubilized native LHRH receptor has a Stokes radius of 52 A and the same, antagonist labeled receptor a radius of 48 A.

Affinity Labels↗
PubMed1995

Fate of mouse macrophages radiolabelled with PKH-95 and injected intravenously.

Mouse macrophages purified by elutriation from thioglycollate-induced peritoneal exudate cells were labelled with indium-111-oxine and injected intravenously into mice. A substantial amount of unbound radioactivity remained in the circulation, suggesting that the radionuclide was not stably bound to the cells. Culture experiments with radiolabelled cells showed that indium-111 was released in the medium. Another cell marker, PKH-95, an iodine-125-labelled aliphatic compound insertable into the cell membrane, bound more stably than indium-111. Five minutes after injection of 125I-PKH-95-labelled macrophages, about 98% of the cells were in a non-circulating pool. It was checked that PKH-95 labelling did not compromise the viability and functions of the macrophages and that autologous erythrocytes and blood mononuclear cells labelled with PKH-95 remained in the circulation after i.v. injection. One hour after injection, 125I-PKH-95-labelled macrophages were distributed mainly in lung (36%), liver (19%) and spleen (5%). Subsequently, radioactivity decreased in the lung while increasing in liver, spleen and in an artificially induced footpad inflammation. The radioactivity accumulation in the inflammation persisted at least for 7 days. It represented a small proportion of radioactivity injected (0.2%) but was trapped very specifically in the inflammation. This raised the hypothesis that macrophages of the non-circulating pool could be released in the circulation and recruited into the inflammation with slow kinetics.

Animals↗
PubMed1996

A review of countermeasures to reduce radioiodine in milk of dairy animals.

The most effective countermeasure for radioiodine contamination of milk is to provide dairy animals with uncontaminated feed, with the added advantage that it will be effective for other radionuclides in the fallout. Another effective response is to process the milk into storable dairy products for an appropriate length of time to allow for physical decay. The use of additives given to ruminants to reduce radioiodine in milk is an alternative countermeasure which could be effective. Stable iodine administration is a practically feasible option which has the potential to reduce radioiodine levels in milk by at most a factor of three. Stable iodine supplementation should be at sufficiently high rates to be effective (and at least 1 g d-1 for dairy cows), particularly for ruminants already receiving high amounts of iodine in the diet. Currently available data are inadequate to recommend a suitable stable iodine administration rate for different species of ruminants. Other compounds, such as perchlorate and thiocyanate, also reduce the transfer to radioiodine to milk (and thyroid). Some of these compounds seem to be potentially equally as effective as stable iodine. However, currently there is inadequate information on their effectiveness and possible toxicity to both ruminants and humans for these compounds to be considered as suitable countermeasure additives.

Animals↗
PubMed1973

Studies on mono- and diiodohistidine. I. The identification of iodohistidines from thyroidal iodoproteins and their peripheral metabolism in the normal man and rat.

The problem as to whether iodohistidines are normally biosynthetized in thyroglobulin and thyralbumin has been examined both in man and the rat. Evidence has been obtained for the first time that diiodohistidine (DIH) is present in both species in these two iodoproteins. The biosynthesis of monoiodohistidine (MIH) in the thyroglobulin of the normal rat has been confirmed and extended to rat thyralbumin and to human thyroid iodoproteins. THE IODOHISTIDINE IDENTIFICATION IS BASED ON FIVE ORIGINAL METHODS INCLUDING: (a) the preparation of stable and radioiodine-labeled iodohistidines; (b) the protection of the labile iodohistidines during the iodoprotein enzymatic hydrolysis; (c) the isolation of iodohistidines by ion-exchange resin chromatography; (d) their separation from each other and from iodinated cationic butanol-insoluble compounds by Sephadex G-10 chromatography; and (e) their purification by successive crystallizations to a constant specific activity. Iodohistidine levels (in percent of protein radioactivity from iodide given in vivo) were found comparable in man and the rat. However, the values (mean +/-SE) for thyroglobulin (MIH, 0.61+/-0.10%; DIH, 0.050+/-0.015%) and for thyralbumin (MIH, 2.61+/-0.57%; DIH, 0.28+/-0.09%) differ significantly (P < 0.05). Iodohistidines are stable during in vitro exposure to iodotyrosine dehalogenase preparations. In contrast to iodotyrosines the iodohistidines when given in vivo to man either orally or intravenously were in large part recovered in 24-h urines.

Administration, Oral↗
PubMed1983

Synthesis of [10S(19)-3H]-dihydrotachysterol2 from ergocalciferol and preliminary investigations into its metabolic fate in rats.

Dihydrotachysterol2 (DHT2), a 5,6-trans derivative of vitamin D2, is very successfully used in the treatment of hypoparathyroidism and renal osteodystrophy. However, the metabolism and the action of DHT2 are poorly understood. Investigations into metabolism of DHT2 start at the synthesis of the radioactively labelled compound. This paper deals with a two-step synthesis of [10S(19)-3H]-dihydrotachysterol2 from vitamin D2. Vitamin D2 can be converted into 5,6-trans vitamin D2 by iodination under irradiation and by triplet-sensitized isomerization. The first method led to unwanted side-reaction products which were difficult to separate from 5,6-trans vitamin D2. Triplet-sensitized isomerization yielded merely 5,6-trans vitamin D2 which could be separated from the residual starting material by chromatography on silica gel and recrystallization. [10S](19)-3H]-Dihydrotachysterol2 with a specific radioactivity of 56 kCi/mol was prepared from 5,6-trans vitamin D2 via partial, homogeneous catalytic reduction of the 10S(19) double bond with tritium gas. It was purified by high-performance liquid chromatography (h.p.l.c.) and characterized by chromatography and ultra-violet absorption spectrophotometry. The biological usefulness of the material was demonstrated in rats following intragastric administration. Blood was collected after 24 and 48 h and fractionation of serum lipids on h.p.l.c. showed 5 peaks of radioactivity.

Animals↗
PubMed1984

Iodinated compounds and thyroxine binding to albumin in human breast milk.

Mature human milk samples from young healthy women on an equilibrated diet contained a mean of 81 ng/ml total iodine. Iodide represented a mean of 77% of the total iodine. Of the 22 ng/ml organic iodine, there was about 1 ng thyroxine and triiodothyronine and, after pepsin hydrolysis, up to 40% of organic iodine in monoiodotyrosine form. By electrophoresis, after incubation with radioactive thyroid hormone, we found an absence of binding on thyroxine-binding globulin, but thyroxine and triiodothyronine were bound to albumin with a maximal capacity 50 times higher than in human serum. All these differences did not favor transport of iodinated compounds from maternal serum to milk. In conclusion, milk iodide was taken up by newborn thyroid to make thyroid hormones.

Albumins↗
PubMed1980

Iodine metabolism and iodothyronine (T3 and T4) binding in human polymorphonuclear leucocytes in vitro.

Surviving human polymorphonuclear leucocytes (PMNL) were found to incorporate and metabolize 125I in vitro. After incubation the metabolized iodine may be found in three different fractions which may be separated by Sephadex G-200 column chromatography. The first fraction consists of deoxyribonucleoproteins and specifically binds T3 (Bmax) 4 x 10(-12) mol mg-1 protein; Ka (4.5 x 10(11) mol-1 mg) and T4 (Bmax) 13 x 10(-12) mol mg-1 protein; Ka (0.77 x 10(11) mol-1 mg). The second fraction binds iodine and T4 by a non displaceable manner. It appears to be acid precipitable and possibly of iodoprotein nature. The third fraction of iodinated molecules was further analyzed with the aid of Sephadex G-10 column chromatography and it was found that these compounds may correspond to iodothyronines, as concluded from their physicochemical characters. The addition of T3 or T4 or TSH reduced the radioactivity associated presumably to nucleoproteins and iodoproteins. These experiments suggest a possibility of intracellular synthesis and macromolecular binding of iodothyronine-like compounds in PMNL and the influence of external T3, T4 and TSH.

Female↗
PubMed2000

Synthesis and use of 3'-(azidoiodosalicyl) derivatives of 2', 5'-dideoxyadenosine as photoaffinity ligands for adenylyl cyclase.

3'-[(4-Azidosalicyl)glycyl]-2',5'-dideoxyadenosine (1), 3'- [(4-azidosalicyl)-gamma-aminobutyryl]-2',5'-dideoxyadenosine (2), and the (125)I-labeled mono- and diiodinated analogs of 1 were synthesized and tested as photoaffinity probes for adenylyl cyclases. Kinetics for inhibition of purified type I enzyme by 1 was noncompetitive with respect to Mn(*)5'-ATP in the absence of light, implying a P-site mechanism of inhibition. In a UV-dependent manner both 1 and 2 and the iodinated derivative of 1 irreversibly inactivated membrane-bound and purified forms of recombinant type I bovine adenylyl cyclase expressed in ovarian cells of either the fall armyworm (Sf9) or Trichoplasia ni (High Five). Irreversible inactivation was independent of 5'-ATP and was prevented by 2', 5'-dideoxyadenosine. Adenylyl cyclase, whether purified from bovine brain or in membranes from High Five cells expressing type I enzyme, when subjected to UV irradiation in the presence of (125)I-labeled 1 resulted in radioactive incorporation into protein migrating at approximately 116 kDa. The cross-linking of 1 and its iodinated derivative with adenylyl cyclase suggests potential for such compounds to be useful in structural studies of adenylyl cyclases or of other proteins for which adenine nucleosides are substrates or allosteric regulators.

Adenosine↗
PubMed1987

Synthesis and biological activities of beta-alanyltyrosine derivative of 2',5'-oligoadenylate, and its use in radiobinding assay for 2',5-oligoadenylate.

beta-Alanyltyrosine derivative of 2',5'-tetraadenylate 5'-triphosphate, pppA2'p5'A2'-p5'A2'p5'A-beta-Ala-Tyr was prepared by coupling of periodate-oxidized pppA2'p5'-A2'p5'A2'p5'A with beta-alanyltyrosine methyl ester, followed by reduction with sodium cyanoborohydride. Its stability to 2',5'-phosphodiesterase and phosphatase was investigated in mouse L cell extract. The 5'-triphosphate of the compound was cleaved gradually to form the 5'-dephosphorylated derivative, A2'p5'A2'p5'A2'p5'A-beta-Ala-Tyr, followed by slow degradation of the 2',5'-phosphodiester bond. On the other hand, pppA2'p5'A2'p5'A2'p5'A was hydrolyzed very quickly under the same conditions. The tetramer derivative bound tightly to the 2',5'-oligoadenylate-dependent endoribonuclease in rabbit reticulocyte lysate or mouse L cell extract and inhibited protein synthesis of mouse L cells more effectively than the unmodified 2',5'-tetraadenylate 5'-triphosphate. The corresponding trimer derivative had slightly weaker activities than the unmodified trimer for binding to the endoribonuclease and for inhibition of protein synthesis. The compound, pppA2'p5'A2'p5'-A2'p5'A-beta-Ala-Tyr, was iodinated easily at the tyrosine residue with 125I, giving a high-specific-radioactivity derivative which was used as a radio-labeled probe in a radiobinding assay for 2',5'-oligoadenylate.

Adenine Nucleotides↗
PubMed1995

Platelet aggregation inhibiting and anticoagulant effects of oligoamines, XXX: Absorption, organ distribution, and excretion of the oligoamine (+)-(S,S)-1,4-bis-[4-(3-iodo-4-methoxyphenyl)-butylamino]-butane-2,3-di ol and its metabolites.

The pharmacokinetic behaviour of the 131-iodine-labelled title compound 3* and its metabolites in mice was investigated. A two phase, 1st order elimination profile was observed. The second phase is very slow leaving about 35% of radioactivity in the mice even 100 h after i.v. injection, because of high affinity to liver and spleen, caused by strong binding of oligoamines to phospholipids of liver and blood cell membranes. The blood-brain-barrier is not passed. No deep compartments were observed. The doses necessary for antithrombotic effects in vivo were calculated from the blood levels to be 20.5-39.7 mumol/kg for a time interval of 1-6 h after administration.

Animals↗
PubMed1988

Influence of specific activity on myocardial uptake of 123I-mIBG in rats.

Heart and lung uptake of 123I-mIBG was studied in rats 1 h after injection as a function of specific activity (mCi mg-1) and the total loading dose (microgram kg-1) of labelled compound. Absolute lung uptake of the tracer was dependent upon specific activity, declining as the loading dose increased from 0.15 to 4300 micrograms kg-1. Uptake in the total heart was constant at 2.1% up to about 12 micrograms kg-1, at which point the heart uptake also began to decline as the loading dose increased. Myocardial uptake of 123I-mIBG, therefore, appears saturable in the rat and subject to competitive binding and/or displacement with increasing amounts of non-labelled compound.

3-Iodobenzylguanidine↗