The biodistribution of [75Se]bis-[β-(N,N,N-trimethylamino)ethyl]selenide diiodide in adult guinea pigs

The biodistribution of [⁷⁵Se]BISTAES was studied in guinea pigs. A higher concentration of radioactivity was observed in articular cartilage than in other tissues or organs. A minimal amount of radioactivity was found in the blood, muscle and bone. The compound was excreted rapidly in urine. The target to background ratios were encouraging. [⁷⁵Se]BISTAES has potential as an articular cartilage imaging agent and further studies in osteoarthritic animals are merited.     

Identification of a selenocysteine-specific aminoacyl transfer RNA from rat liver

The aminoacylation of rat liver tRNA with selenocysteine was studied in tissue slices and in a cell-free system with [⁷⁵Se]selenocysteine and [⁷⁵Se]selenite as substrates. [⁷⁵Se]Selenocysteyl tRNA was isolated via phenol extraction, 1 M NaCl extraction and chromatography on DEAE-cellulose. [⁷⁵Se]Selenocysteyl tRNA was purified on columns of DEAE-Sephacel, benzoylated DEAE-cellulose and Sepharose 4B. In a dual-label aminoacylation with [³⁵S]cysteme, the most highly purified ⁷⁵Se-fractions were > 100-fold purified relative to ³⁵S. These fractions contained < 0.7% of the [³⁵S]cysteine originally present in the total tRNA. When [³⁵Se]selenocysteyl tRNA was purified from a mixture of ¹⁴C-labeled amino acids, over 97% of the [¹⁴C]aminoacyl tRNA was removed. The [⁷⁵Se]selenocysteine was associated with the tRNA via an aminoacyl linkage. Criteria used for identification included alkaline hydrolysis and recovery of [⁷⁵Se]selenocysteine, reaction with hydroxylamine and recovery of [⁷⁵Se]selenocysteyl hydroxamic acid and release of ⁷⁵Se by ribonuclease. The specificity of [⁷⁵Se]selenocysteine aminoacylation was demonstrated by resistance to competition by a 125-fold molar excess of either unlabeled cysteine or a mixture of the other 19 amino acids in the cell-free selenocysteine aminoacylation system.     

Selenium-mediated biochemical changes in Japanese quails

The tissue uptake and distribution of injected [⁷⁵Se]-sodium selenite as a variance with time and as influenced by dietary selenium status was followed in the tissues of Japanese quails,Coturnix coturnix japonica. Quails maintained on a low selenium semipurified (basal) diet and basal diets supplemented with 0.2 and 2.0 ppm selenium as sodium selenite were injected intraperitonially with⁷⁵Se as sodium selenite (2.8 microcuries). The injected⁷⁵Se was monitored in blood, liver, kidney, heart, and testis at 24, 72, and 144 h after injection. Maximal uptake of the injected⁷⁵Se was observed in tissues of quails maintained on basal diet. The uptake of⁷⁵Se in tissues in general was determined by the dietary Se status. Among the organs studied, kidney had the maximal level of⁷⁵Se, 0.2 ppm (μg/g wet tissue) followed by liver, testis, and heart, but testis had the maximal level when the level per milligram of protein was considered, about 3.0 ng/mg protein, followed by liver, kidney, and heart. About 10–20% of the tissue⁷⁵Se was located in the mitochondria and 50–60% in the post-mitochondrial supernatant fractions in all dietary Se levels. Significant incorporation of⁷⁵Se in the mitochondrial membrane was observed. The percent distribution ratio between the membrane and matrix fractions of the mitochondria remained constant at all dietary Se levels which, in liver was 65∶35, in kidney 55∶45, and in testis 75∶25. However, in heart mitochondria, the distribution of⁷⁵Se between membrane and matrix varied with dietary Se status, the ratio being 82∶18 in the basal group, and 72∶28 and 41∶59 in the 0.2 and 2.0 ppm Se-supplemented groups, respectively. This is indicative of a preferential uptake of⁷⁵Se in the mitochondrial membrane in conditions of deficiency. About 40–60% of the mitochondrial membrane-associated⁷⁵Se was released upon Triton treatment in all the organs. Of the membrane-bound⁷⁵Se, about 10–15% was acid-labile in liver and kidney and 25% in the heart tissue. Possibilities of tissue specific roles, especially in the heart mitochondrial membrane-related processes, are indicated for selenium.     

Kinetic analysis of75selenium uptake by mitochondria of germinating vigna radiata of different selenium status

Earlier studies in our laboratory demonstrated the beneficial role of Se inVigna radiata, a Se-deficient legume, during germination, as reflected in growth-related parameters and specific uptake of⁷⁵Se. Uptake of Na₂ ⁷⁵SeO₃, added in vitro by mitochondria isolated from seedlings germinated in control (without Se), and Se-supplemented groups (0.5, 1.0, and 2.0 ppm Se) indicated a proportional increase in the uptake with added Na₂ ⁷⁵SeO₃, in concentrations up to 25 γM. The uptake of⁷⁵Se, increased linearly with time up to 15 min and a definite efflux followed at 30 min. The results were indicative of cooperative effects during Se transport. Kinetic analyses of the uptake of⁷⁵Se during time intervals of 15 and 30 min were carried out both in the whole mitochondria and the mitochondrial protein fractions. Graphical analyses using Lineweaver-Burk plot, Hill plot, log [v] vs log [A] and Scatchard plot confirmed the existence of negative cooperativity during⁷⁵Se uptake. Hill coefficient (nH) values were estimated to be around 0.7–0.8. Scatchard plots for⁷⁵Se uptake were biphasic, suggesting the probable presence of two classes of binding sites. The number of high and low affinity binding sites were estimated to be around 4–7 and 26–30 nmol/mg protein, respectively. Studies with mitochondrial respiratory inhibitors indicated about 10–20% of the total⁷⁵Se uptake to be energy dependent. Inhibition of⁷⁵Se uptake by about 60–70% by sulfate and sulfite (5–25 γM) implies the involvement of dicarboxylate port in Se transport. A decrease in the uptake of⁷⁵Se by 40–60% effected by CdCl₂, HgCl₂, mersalyl, and NEM confirmed the interaction of thiols in the process. Evidence for the regulatory nature of⁷⁵Se uptake by mitochondria ofV. radiata emerges from the present study.     

Biodistribution of bis[β-(N,N,N-trimethylamino)ethyl]selenide-75Se diiodide,a potential articular cartilage imaging agent

In an effort to develop a specific radiodiagnostic agent for articular cartilage imaging, we have investigated the biodistribution of bis[β-(N,N,N-trimethylamino)ethyl]selenide-⁷⁵Se diiodide (⁷⁵Se BISTAES) in rabbits. At an intravenous dose of 5 mg/kg, the greatest localization of the compound occurred in articular cartilage 15 min after injection. The compound was excreted rapidly in the urine. The results suggest that ⁷⁵Se BISTAES has potential clinical use as an articular cartilage imaging agent.     

Selenium compounds in the fathead minnow (Pimephales promelas)--I. Uptake, distribution, and elimination of orally administered selenate, selenite and l-selenomethionine

Treatment of fathead minnows (Pimephales promelas) with either [75Se]selenate, -selenite or -l-selenomethionine by gavage at 20 ng Se/g resulted in organ uptake and early distribution patterns which differed significantly between compounds. The greatest differences in uptake between compounds was observed in liver tissue which accumulated much less [75Se]selenate than either selenite or l-selenomethionine. The 75Se burdens and relative distribution among the various organs were nearly identical during the elimination phase for [75Se]selenate and -selenite. This suggests that selenium derived from these compounds converge to a common metabolic pool. The whole body T1/2, rate of 75Se uptake and magnitude of 75Se accumulation were generally greater for [75Se]selenomethionine than the inorganic forms. Selenium-75 was present in the bile following the oral administration of each compound. The partitioning of selenate and selenite into the plasma and cellular fraction of blood differs with both the compound and time following exposure.     

In vitro synthesis of glutathione peroxidase from selenite Translational incorporation of selenocysteine

The synthesis of glutathione peroxidase from [⁷⁵Se]selenite was studied in slices and cell-free extracts from rat liver. The incorporation of [⁷⁵Se]selenocysteine at the active site was detected by carboxymethylation and hydrolysis of partially purified glutathione peroxidase (glutathione:hydrogen peroxide oxidoreductase, EC 1.11.1.9) in the presence of [³H]selenocysteine and subsequent amino acid analysis. The synthesis of glutathione peroxidase in slices was inhibited by cycloheximide or puromycin and ⁷⁵Se was incorporated from [⁷⁵Se]selenite into free selenocysteine and selenocysteyl tRNA. Increasing concentrations of selenocystine caused a progressive dilution of the ⁷⁵Se and a corresponding decrease in glutathione peroxidase labeling. In cell-free systems, [⁷⁵Se]selenocysteyl tRNA was the best substrate for glutathione peroxidase synthesis. These results indicate the existence in rat liver of the de novo synthesis of free selenocysteine and a translational pathway of selenocysteine incorporation into glutathione peroxidase     

Uptake of selenium-75 by PHA-stimulated lymphocytes

To determine which of a variety of inorganic and organic selenium compounds could best stimulate glutathione peroxidase, human lymphocytes were cultured with a number of selenium sources. The phytohemagglutinin-transformed lymphocytes were cultured in the presence of⁷⁵Se bound to serum proteins (25% v/v) or 10^?7 M concentrations of [⁷⁵Se]-selenite, [⁷⁵Se]-selenate, [⁷⁵Se]-selenocystine, and [⁷⁵Se]-selenomethionine. Organic forms of selenium were taken up in preference to inorganic forms. Control cultures, from which exogenous selenium had been omitted, showed a decreased level of glutathione peroxidase activity at the end of a 4 d culture period. Of the Se sources tested, [⁷⁵Se]-selenocystine and [⁷⁵Se]-labeled fetal calf serum proteins increased enzyme activity significantly, 79 and 47%, respectively, but selenite increased activity only by 7%. These results indicate that selenium from the two organic sources is most readily available for glutathione peroxidase synthesis.     

UPTAKE AND RELEASE OF TAURINE FROM CEREBRAL CORTEX SLICES AND THEIR SUBCELLULAR COMPARTMENTS

—Cortex slices, synaptosomes and C-6 glioma cells were used to study [³⁵S]taurine uptake and its electrically-stimulated release. After exposure to taurine at two concentrations, the synaptosome preparation subsequently derived from the slices contained 41% of the particle-bound taurine and 16% of the total in the tissue. The uptake of [¹⁴C]GABA by C-6 glioma cells was inhibited 3-fold more by β-alanine than by l -DABA, whilst synaptosome preparations showed the opposite pattern, l -DABA being 2 or 3 times more effective than β-alanine. [³⁵S]Taurine uptake inhibition by l -DABA was low for synaptosomes and C-6 glioma, whereas β-alanine showed considerable effect on C-6 glioma (41%) and slices of white matter (ependyma; 50%). Synaptosome preparations showed little effect with β-alanine. When 30 min rather than 5 min incubations were employed, β-alanine depressed [³⁵S]taurine uptake by cortex slices by 30%. Taurine was taken up by a calcium-dependent mechanism and subcellular fractionation indicated that the synaptosome fraction showed losses commensurate with the net taurine release when low stimulation currents were used.     

In Vitro Incorporation of Selenomethionine into Protein by Vigna radiata Polysomes

Vigna radiata polysomes efficiently incorporated [⁷⁵Se]selenomethionine, [¹⁴C]methionine, and [¹⁴C]leucine in vitro. The optimal conditions for translation were determined to be 4.8 millimolar Mg²⁺, 182 millimolar K⁺, and pH 7.4. The rates of incorporation of [⁷⁵Se]selenomethionine and [¹⁴C]methionine were similar when measured separately, but [⁷⁵Se]selenomethionine incorporation was 35% less than [¹⁴C]methionine incorporation when both amino acids were present in equal molar concentrations. Polyacrylamide gel electrophoresis of the hot trichloroacetic acid precipitable translation products demonstrated synthesis of high molecular weight labeled proteins in the presence of [⁷⁵Se]selenomethionine or [³⁵S]methionine. No major differences in molecular weights could be detected in the electrophoretic profiles. Utilization of selenomethionine during translation by Vigna radiata polysomes establishes a route for the assimilation of selenomethionine by plants susceptible to selenium toxicity.     

Selenite uptake and incorporation by Selenomonas ruminatium

Selenite uptake and incorporation in Selenomonas ruminantium was constitutive with an inducible component. It was distinct from sulphate or selenate transport, since sulphate and selenate did not inhbit uptake, nor could sulphate or selenate uptake be demonstrated. Selenite uptake had an apparent K _m of 1.28 mM and a V _max of 148 ng Se min^-1 mg^-1 protein. Uptake was sensitive to inhibition by 2,4-dinitrophenol (DNP), carbonyl cyanide m-chlorophenyl hydrazone (CCCP), azide, iodoacetic acid (IAA) and N-ethylmaleimide (NEM), but not chloropromazine (CPZ), N,N-dicyclohexyl-carbodiimide (DCCD), quinine, arsenate, or fluoride. Treatment of cells accumulating ⁷⁵[Se]-Selenite with 2,4,DNP inhibited uptake, but did not cause efflux. Transport of selenite was inhibited by sulphite and nitrite, but not by nitrate, phosphate, sulphate of selenate. ⁷⁵[Se]-Selenite was incorporated into selenocystine, selenoethionine, selenohomocysteine, and selenomethionine and was also reduced to red elemental selenium.     

Ubiquity of selenium-containing tRNA in plants

Sodium[⁷⁵Se]selenite supplemented culture of Chlamydomonas, wild carrot, tobacco, bamboo, and rice cells as well as mung bean and soybean seedlings incorporated, without exception, ⁷⁵Se into tRNAs. The content of ⁷⁵Se-labeled tRNAs ranged from 0.04 to 1.89% of the total tRNAs in these seven plant species. [⁷⁵Se]tRNA samples of wild carrot and mung bean were fractionated into six or seven seleno-tRNA species by chromatography on RPC-5 column. Samples of tobacco, bamboo and Chlamydomonas each exhibited only a single seleno-tRNA species with a close interspecific resemblance in the elution position among the three samples. All these [⁷⁵Se]tRNAs contained a new, not yet identified ⁷⁵Se-labeled nucleoside, whose retention time on HPLC was distinctly different from that of the previously reported bacterial selenonucleosides. [⁷⁵Se]tRNA samples of rice, tobacco, bamboo, mung bean and Chlamydomonas also contained one or two minor ⁷⁵Se-labeled nucleosides. These results suggest that (1) selenium-containing tRNAs appear to be widespread in the plant kingdom and (2) a new, not yet characterized selenonucleoside might be universal in plants.     

Synthesis and radiobiological applications of [35S]l-homocysteine thiolactone

[³⁵S]l-Homocysteine thiolactone ([³⁵S]l-HCTL) was synthesized and its biodistribution evaluated as a potential brain radioprotective agent and as a tissue hypoxia marker. Drug uptake in mouse brain exceeded that in s.c. tumor 3 h post injection only. Multiple indicator dilution experiments in the rabbit heart indicate that membrane permeability of [³⁵S]l-HCTL does not limit its usefulness as a hypoxia marker. In addition, a positive correlation was observed between regional coronary blood flow and myocardial content of [³⁵S]adenosylhomocysteine formed from [³⁵S]homocysteine and adenosine.     

(+)-[C-11]-cis-N-benzyl-normetazocine: A selective ligand for sigma receptors in vivo

The in vivo biodistribution profile of the novel sigma (σ) receptor ligand (+)-[C-11]-cis-N-benzyl-normetazocine ([C-11]-(+)-NBnNM) in mouse brain was examined. This radioligand displayed high brain uptake and a distribution consistent with the density of σ receptors. Brain radioactivity levels peaked at 15 min postinjection and were largely maintained (ca. 80% of maximal values) up to 90 min postinjection. Pretreatment with several different σ ligands (haloperidol, (+)-pentazocine, DuP 734, ifenprodil) effectively inhibited [C-11]-(+)-NBnNM binding in a dose-dependent manner in all brain regions. [C-11]-(+)-NBnNM binding sites were shown to be saturable with unlabeled (+)-NBnNM (ED50 = 0.02 mg/kg) and enantioselectively inhibited by the optical isomers of pentazocine. A blocking dose of the dopamine D2 antagonist spiperone (1 mg/kg) did not significantly inhibit [C-11]-(+)-NBnNM binding. Pretreatment with the phencyclidine (PCP) blocker 1-[1-(2-thienyl)cyclohexyl] piperidine (TCP) did not significantly alter total brain tissue radioactivity. Thus, [C-11]-(+)-NBnNM binds with high specificity and selectivity to σ receptors in vivo and offers excellent potential to study σ receptors in living human brain via positron emission tomography.     

Regional distribution study of brain perfusion and metabolic agents in normal and tumour bearing rat brains using autoradiographic technique

Regional distribution of brain perfusion imaging agents, [¹³¹I]N,N,N′-trimethyl-N′-[2-hydroxy-3-methyl-5-iodobenzyl]1,3 propanediamine (HIPDM) and [¹³¹I]N-isopropyl-p-iodoamphetamine (IMP), was compared with the distribution of patterns of [¹⁴C]l-methionine and [¹⁴C]d-glucose in normal and tumour bearing rat brains using autoradiographic technique. There was higher concentration of the radiopharmaceutical in grey than white matter in normal rat brain. Autoradiographs of brain tumour sections showed very low uptake of [¹³¹I]HIPDM and [¹³¹I]IMP as compared to normal brain tissue. There was moderate concentration of [¹⁴C]d-glucose and avid uptake of [¹⁴C]l-methionine in tumours. Autoradiographic study is useful for evaluating distribution patterns of radiopharmaceuticals.     

Uptake of GABA by neuronal and nonneuronal cells in dispersed cell cultures of postnatal rat cerebellum

A study was made of the time course and kinetics of [³H]GABA uptake by dispersed cell cultures of postnatal rat cerebellum with and without neuronal cells. The properties of GABA neurons were calculated from the biochemical difference between the two types of cultures. It was found that for any given concentration of [³H]GABA, or any time up to 20 min, GABA neurons in cultures 21 days in vitro had an average velocity of uptake several orders of magnitude greater than that of nonneuronal cells. In addition, the apparent K_m values for GABA neurons for high and low affinity uptake were 0.33 × 10⁻⁶ M and 41.8 × 10⁻⁴ M, respectively. For nonneuronal cells, the apparent K_m for high affinity uptake was 0.29 × 10⁻⁶ M. The apparent V_max values for GABA neurons for high and low affinity uptake were 28.7 × 10⁻⁶ mol/g DNA/min and 151.5 mmol/g DNA/min, respectively. For nonneuronal cells, the apparent V_max for high affinity uptake was 0.06 × 10⁻⁶ mol/g DNA/min. No low affinity uptake system for nonneuronal cells could be detected after correcting the data for binding and diffusion. By substituting the apparent kinetic constants in the Michaelis-Menten equation, it was determined that for GABA concentrations of 5 × 10⁻⁹ M to 1 mM or higher over 99% of the GABA should be accumulated by GABA neurons, given equal access of all cells to the label. In addition, high affinity uptake of [³H]GABA by GABA neurons was completely blocked by treatment with 0.2 mM ouabain, whereas that by nonneuronal cells was only slightly decreased. Most (75–85%) of the [³H]GABA (4.4 × 10⁻⁶ M) uptake by both GABA neurons and nonneuronal cells was sodium and temperature dependent.     

Uptake of selenite,selenomethionine and selenate by brush border membrane vesicles isolated from rat small intestine

The uptake of selenite, selenate and selenomethionine (SeMet) was performed with brush border membrane vesicles (BBMV) prepared from rats fed selenium-deficient and supplemented diets. At equilibrium (60 min), the uptake of ⁷⁵Se from [⁷⁵Se]selenite ranged from 16.5 to 18.9 nmol mg^-1 protein. There was a curvilinear relationship in the uptake of selenite over a concentration range of 10–1000 m. About 2 nmol mg^-1 protein was obtained with selenomethionine (SeMet) which occurred between 90 and 180 s. In contrast to selenite, there was a linear relationship in the initial uptake of SeMet over a concentration range of 10–1000 m. The uptake of selenate was approximately 50-fold lower than selenite, reaching 350 pmol mg^-1 protein. Dietary selenium level had no effect on the rate of ⁷⁵Se accumulation by BBMV. Dramatic differences are found in the uptake and binding of selenium by BBMV incubated with different selenocompounds.     

Metabolic relevance of selenium in the insectCorcyra cephalonica

Requirement, uptake, and subcellular distribution of Na₂ ⁷⁵SeO₃ in the larvae of the insectC. cephalonica was investigated. That Se is well tolerated byC. cephalonica upto an added level of 2 ppm in the diet is suggested by the observed increase in body weight, total protein, and succinate dehydrogenase levels. Significant increases in the State 3 respiration ensued with Se supplementation up to 2 ppm in the mitochondrial oxidation of D-glycerol 1-phosphate, succinate and NADH, along with concomitant unaltered State 4 respiration, leading to enhanced RCR values. Maximal uptake of⁷⁵Se was registered in the larvae maintained on basal diet when subjected to short-term exposure to 0.5 ppm⁷⁵Se level. When exposure level was further increased up to 20 ppm, the observed decrease in the uptake of⁷⁵Se suggested that Se status of larvae itself controlled the tissue uptake. Subcellular distribution pattern revealed maximal incorporation of⁷⁵Se (cpm/g tissue) in the supernatant fraction, whereas, maximal specific⁷⁵Se activity (cpm/mg protein) was associated with the mitochondrial fraction. Autoradiography of the soluble fractions indicated the presence of single selenoprotein in the larval group with short term 2 ppm⁷⁵Se exposure. Inherent Se controls both the extent and the nature of distribution of mitochondrial⁷⁵Se incorporation. Uptake of⁴⁵Ca by the insect mitochondria was enhanced by dietary Se up to 2 ppm but was unaffected by addition ofin vitro ⁷⁵Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies.     

Imaging Axl expression in pancreatic and prostate cancer xenografts

The receptor tyrosine kinase Axl is overexpressed in and leads to patient morbidity and mortality in a variety of cancers. Axl–Gas6 interactions are critical for tumor growth, angiogenesis and metastasis. The goal of this study was to investigate the feasibility of imaging graded levels of Axl expression in tumors using a radiolabeled antibody. We radiolabeled anti-human Axl (Axl mAb) and control IgG1 antibodies with ¹²⁵I with high specific radioactivity and radiochemical purity, resulting in an immunoreactive fraction suitable for in vivo studies. Radiolabeled antibodies were investigated in severe combined immunodeficient mice harboring subcutaneous CFPAC (Axl^high) and Panc1 (Axl^low) pancreatic cancer xenografts by ex vivo biodistribution and imaging. Based on these results, the specificity of [¹²⁵I]Axl mAb was also validated in mice harboring orthotopic Panc1 or CFPAC tumors and in mice harboring subcutaneous 22Rv1 (Axl^low) or DU145 (Axl^high) prostate tumors by ex vivo biodistribution and imaging studies at 72 h post-injection of the antibody. Both imaging and biodistribution studies demonstrated specific and persistent accumulation of [¹²⁵I]Axl mAb in Axl^high (CFPAC and DU145) expression tumors compared to the Axl^low (Panc1 and 22Rv1) expression tumors. Axl expression in these tumors was further confirmed by immunohistochemical studies. No difference in the uptake of radioactivity was observed between the control [¹²⁵I]IgG1 antibody in the Axl^high and Axl^low expression tumors. These data demonstrate the feasibility of imaging Axl expression in pancreatic and prostate tumor xenografts.     

High-Affinity Uptake of [3H]Norepinephrine by Primary Astrocyte Cultures and Its Inhibition by Tricyclic Antidepressants

Abstract: Primary astrocyte cultures from neonatal rat brains show uptake of [³H]norepinephrine ([³H]NE). This uptake has a high-affinity component with an apparent K_m of approximately 3 × 10^?7 M. At 10^?7 M [³H]NE both the initial rate of uptake and steady-state content of [³H]NE is inhibited by up to 95% by omission of external Na⁺. The Na⁺-dependent component of this uptake is totally inhibited by the tricyclic antidepressants desipramine (DMI) and amitryptyline with IC₅₀ values of 2 × 10^?9 and 4 × 10^?8 M, respectively. Inhibition of [³H]NE uptake by DMI shows competitive kinetics. These characteristics are essentially identical to those found for high-affinity uptake of NE in total membrane or synaptosome fractions from rodent brains and suggests that such uptake in neural tissue is not exclusively neuronal.