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N Seiler

Publications and source records attributed to N Seiler.

At least 19 recordsLinked to original sources
PubMed1992

Antagonism of phencyclidine-induced hyperactivity in mice by elevated brain GABA concentrations.

Vigabatrin and (S)-4-allenylGABA (MDL 72483), two anticonvulsant GABA-T inhibitors, partially antagonize phencyclidine (PCP)-induced hyperactivity in mice at doses that do not affect spontaneous motor activity. The PCP antagonism is related to whole-brain GABA concentrations. The results indicate the potential use of GABA-T inhibitors in the therapy of PCP intoxications and perhaps also in the treatment of certain forms of endogenous psychoses.

Aminocaproates↗
PubMed1992

Inhibition of ornithine aminotransferase by 5-fluoromethylornithine: protection against acute thioacetamide intoxication by elevated tissue ornithine levels.

5-Fluoromethylornithine (5FMOrn) is a selective inactivator of ornithine aminotransferase. Its administration causes a dramatic increase of ornithine concentrations in all tissues. Treatment of mice with 20 mg.kg-1 5FMOrn shortly before or after a lethal dose (600 mg.kg-1, intraperitoneally) of thioacetamide (TAA), followed by a second dose 24 hr later, prevented death of 60% of the mice. Pathologic symptoms of TAA intoxication (liver haemorrhage, elevation of amino acids in blood and tissues, diminution of liver spermidine and spermine concentrations, elevation of the activity of liver enzymes in the plasma) were significantly ameliorated by the treatment. The liver protective action of 5FMOrn is related to the elevation of ornithine concentration, as appears from the fact that other, less selective inactivators of ornithine aminotransferase, also produced some protection against acute intoxication with TAA, but not a structurally related compound with no effect on this enzyme.

Amino Acids↗
PubMed1991

Growth inhibition of two solid tumors in mice, caused by polyamine depletion, is not attended by alterations in cell-cycle phase distribution.

We studied the effect of polyamine depletion on growth and cell cycle characteristics of subcutaneously grown Lewis lung carcinoma (LLC) and fibrosarcoma (FIO 26) in mice. Polyamine depletion was achieved by inhibition of ornithine decarboxylase using 2-(difluoromethyl)ornithine, limitation of exogenous polyamines by administration of a polyamine-poor diet and decontamination of the gastrointestinal tract, and inhibition of endogenous polyamine reutilization by N,N'-bis-(2,3-butadienyl)putrescine (MDL 72527). Determination of S-phase cells was performed in tumor-cell suspensions by flow cytometry and in tumor tissue sections by microscopy, following in vivo labelling with 5-bromo-2'-deoxyuridine (BUdR). DNA synthesis rate was estimated from the incorporation of in vivo-injected [3H]-thymidine (3H-TdR). Both solid tumors almost completely stopped growing after access to polyamines was blocked. Growth inhibition was, however, not attended by changes in cell-cycle-phase distribution. Paradoxically, we measured increased in vivo 3H-TdR incorporation rates and unaltered BUdR-linked staining intensity in treated tumors. Injection of putrescine into treated LLC-bearing mice resulted in an increase in intracellular putrescine and spermidine concentrations, a slight increase in the number of S-phase cells and a marked drop in DNA synthesis rate within the following 9 hr.

Animals↗
PubMed1991

(4S)-4-amino-5,6-heptadienoic acid (MDL 72483): a potent anticonvulsant GABA-T inhibitor.

(4S)-4-Amino-5,6-heptadienoic acid [S)-gamma-allenyl-GABA; MDL 72483) is a potent inactivator of brain GABA-T in mice; (ED50 (i.p.) = 60 mg.kg-1; ED50 (oral) = 70 mg.kg-1). Its anticonvulsant effects against 3-mercaptopropionic acid (MPA)-induced seizures in mice is related to the elevation of whole brain GABA concentrations: The mentioned doses of MDL 72483 which cause a decrease of GABA-T activity by 50%, produce within 5 h after dosing an increase of GABA concentration by about 3 mumol.g-1, and protect 50% of the mice against seizures in this model of presynaptic GABA deficit. When given orally MDL 72483 is about five times more potent than vigabatrin [4R/S)-4-amino-5-hexenoic acid) a known antiepileptic GABA-T inhibitor. Complete protection was achieved with a dose of 150 mg.kg-1. Similar to vigabatrin, MDL 72483 does not protect significantly against metrazol-induced convulsions. However, at a dose of 300 mg.kg-1, the time elapsing between metrazol administration and onset of convulsions was prolonged by a factor of 3.4. Oral administration of MDL 72483 for up to 19 days at a daily dose of 91-96 mg.kg-1 did not produce any obvious behavioral changes in mice, nor was the ED50 of the drug in MPA-seizure tests significantly altered by the pretreatment. These observations indicate that MDL 72483 is a promising drug for the treatment of certain epilepsies.

3-Mercaptopropionic Acid↗
PubMed1991

On the degradation and elimination of spermine by the vertebrate organism.

1. Treatment of mice and rats with the polyamine oxidase inhibitor N1,N4-bis-(2,3-butadienyl)-1,4-butanediamine (MDL 72527) causes a gradual accumulation of spermine in the circulation and a decrease of spermidine concentration. 2. Spermine is mainly localized in the red blood cells. 3. Co-administration of 2-(difluoromethyl)ornithine and MDL 72527 enhances considerably the rate and extent of spermine accumulation in the circulation. 4. It is assumed that the increased rate of spermine accumulation by the two drugs is due to the enhancement of cell death, i.e. spermine accumulation is the result of its release into the circulation from dying cells, not due to physiological release. 5. After discontinuation of polyamine oxidase inhibition spermine appears to be gradually transformed into spermidine by red blood cell polyamine oxidase, obviously without transformation into N1-acetylspermine.

Animals↗
PubMed1991

Effects of basic fibroblast growth factor on the development of GABAergic neurons in culture.

Six-day-old neuronal cultures derived from 14-day-old embryonic rat cerebral hemispheres were highly enriched in GABAergic neurons, as was demonstrated by immunocytochemistry using an anti-glutamate decarboxylase antiserum. They contained about 64% glutamate decarboxylase-positive neurons. About 8% of these neurons proliferated, as shown by a combination of glutamate decarboxylase immunocytochemistry and [3H]thymidine incorporation into cell nuclei. The proliferative activity of GABAergic precursor cells and changes in the cellular concentrations of the non-essential amino acids, including GABA under the effect of basic fibroblast growth factor were studied. When basic fibroblast growth factor was added to the cultures 4 h after seeding, the proliferation of the GABAergic neurons was stimulated about threefold. Under this culture condition, the concentration per cell of all amino acids increased, except those of GABA and beta-alanine. When basic fibroblast growth factor was added to cultures only on day four, the proliferation of the neuronal cells was no more enhanced. Under this condition of treatment, the concentrations of all non-essential amino acids, including those of GABA and beta-alanine were enhanced. Under both basic fibroblast growth factor treatments the concentration of GABA per GABAergic cell was increased. In contrast, the specific activity of glutamate decarboxylase was not stimulated under these conditions. We hypothesize that under the effect of basic fibroblast growth factor the capabilities of the cells to store GABA are improved.

4-Aminobutyrate Transaminase↗
PubMed1991

The growth of MAT-LyLu rat prostatic adenocarcinoma can be prevented in vivo by polyamine deprivation.

The combination of inhibitors of ornithine decarboxylase and polyamine oxidase, and of antibiotics suitable for the (partial) decontamination of the gastrointestinal tract, with a polyamine deficient diet, is responsible for the almost complete inhibition of the growth of MAT-LyLu prostatic adenocarcinoma. In the tumor-bearing animals, erythrocyte spermidine levels were reduced, but spermine concentrations were increased. As has been previously observed, the increase in erythrocyte spermine level was associated with an enhancement of malignant cell death. Adriamycin administration did neither diminish tumor growth, nor potentiate the antitumor effect of polyamine deprivation treatment. Interruption of the polyamine deprivation treatment was accompanied by a significant enhancement of tumor growth. Since polyamine deprivation causes only reversible growth inhibition, it seems not appropriate as a monotherapy.

Adenocarcinoma↗
PubMed1990

Endogenous and exogenous polyamines in support of tumor growth.

The combination of inhibitors of ornithine decarboxylase and polyamine oxidase and of antibiotics suitable for the (partial) decontamination of the gastrointestinal tract with a polyamine-deficient diet reduced the growth rate of Lewis lung carcinoma by more than 80%. The formation of lung metastases was prevented by 70 to 100%, depending on the treatment. The reduction of tumor growth was accompanied by a decrease of tissue polyamine concentrations, a reduced rate of tumor cell proliferation, and protein synthesis. The comparison of the ornithine decarboxylase inhibitors Eflornithine [D,L-2-(difluoromethyl)ornithine] and (E)-2-(fluoromethyl)dehydroornithine ethylester confirmed the greater in vivo potency of the latter compound. Our method of growth inhibition by systematic polyamine deprivation is not tumor specific, but presumably generally applicable to rapid growth.

Animals↗
PubMed1990

Potentiation of gamma-vinyl GABA (vigabatrin) effects by glycine.

Vigabatrin, because of its ability to increase brain GABA concentration, acts as an anticonvulsant on convulsive epileptic seizures and increases seizures in generalized non-convulsive epilepsy. Next to GABA, glycine is one of the most important inhibitory neurotransmitter amino acids. We studied the influence of glycine on the effects of treatment with vigabatrin in two rat models of generalized convulsive seizures and a rat model of spontaneous generalized non-convulsive seizures. Glycine (750 mg/kg i.p.) or vigabatrin (200 mg/kg i.p.), when given alone, provided partial protection against convulsive seizures, while combined treatment with the two drugs significantly suppressed the convulsive seizures in both the mercaptopropionic acid (MPA)-induced seizures and audiogenic seizures. In contrast to the response to treatment with each individual drug, the drug combination nearly abolished the appearance of isolated spikes on the EEG in MPA seizures. On the other hand, glycine also enhanced the aggravating effect of vigabatrin on spontaneous spike and wave discharges in a rat model of genetic absence epilepsy, whereas glycine or vigabatrin alone, at the above doses, produced only a slight, non-significant increase in spontaneous spike and wave discharges. The GABA-glycine interaction is the first example of a synergistic action of two inhibitory neurotransmitters on seizure-related pathological discharges.

3-Mercaptopropionic Acid↗
PubMed1990

DL-canaline and 5-fluoromethylornithine. Comparison of two inactivators of ornithine aminotransferase.

5-Fluoromethylornithine (5FMOrn) is an enzyme-activated irreversible inhibitor or ornithine aminotransferase (L-ornithine:2-oxo-acid 5-aminotransferase, OAT). For purified rat liver OAT, Ki(app.) was found to be 30 microM. and tau 1/2 = 4 min. Of the four stereomers of 5FMOrn only one reacts with OAT. The formation of a chromophore with an absorption maximum at 458 nm after inactivation of OAT by 5FMOrn suggests the formation of an enamine intermediate, which is slowly hydrolysed to release an unsaturated ketone. L-Canaline [(S)-2-amino-4-amino-oxybutyric acid] is a well-known irreversible inhibitor of OAT. Not only the natural L-enantiomer but also the D-enantiomer reacts by oxime formation with pyridoxal 5'-phosphate in the active site of the enzyme, although considerably more slowly. This demonstrates that the stereochemistry at C-2 of ornithine is not absolutely stringent. In vitro, canaline reacted faster than 5FMOrn with OAT. In vivo, however, only incomplete OAT inhibition was observed with canaline. Whereas intraperitoneal administration of 10 mg of 5FMOrn/kg body wt. to mice was sufficient to inactivate OAT in brain and liver by 90% for 24 h, 500 mg of DL-canaline/kg body wt. only produced a transient inhibition of 65-70%. The accumulation of ornithine in these tissues was considerably slower and the maximum concentrations lower than were achieved with 5FMOrn. It appears that DL-canaline, in contrast with 5FMOrn, is not useful as a tool in studies of biological consequences of OAT inhibition.

Aminobutyrates↗
PubMed1990

A sensitive method for the assay of glutamine synthetase.

The method for the assay of glutamine synthetase (GlnS) relies on the gamma-glutamyl transferase reaction, i.e. the formation of glutamyl-gamma-hydroxamate from glutamine and hydroxylamine, and the chromatographic separation of the reaction product from the reactants. The method is not only simple and reliable, but also has a sensitivity comparable to those methods applying radioactively labelled substrates. This new procedure has been applied to the assay of GlnS in cultured rat cortical astroglial cells which have been treated with a homologous series of alpha, omega-bis-(dimethylamino)alkanes. Effects of these drugs on astroglial development are reported.

Alkanes↗
PubMed1990

Effects of a series of homologous alpha,omega-dimethylaminoalkanes on cell proliferation: binding and uptake of putrescine by a human glioblastoma cell line (U251) in culture.

The first step of polyamine uptake is the binding of polyamines to the cell membrane. In order to characterize the specificity of the putrescine binding sites at the surface of the glioblastoma cells (U251), we have carried out competition experiments between putrescine bound to latex microspheres and vizualized by scanning electron microscopy and a series of N,N'-tetramethyl-alpha,omega-diaminoalkanes. N,N'-tetramethyl-1,4-butanediamine (N,N'-tetramethylputrescine) and higher homologs inhibit the latex putrescine binding to the cell surface and concomitantly cell proliferation. [14C] putrescine uptake was mainly inhibited by the lower homologs, which were devoid of antiproliferative effects. Our results suggest that putrescine uptake by the human glioblastoma cell line U251, and putrescine binding to the surface of these cells are independent processes. The potential relationship between antitumor effect of N,N'-tetramethyl-alpha,omega-diaminoalkanes and its binding to a specific putrescine acceptor site is discussed.

Binding Sites↗
PubMed1990

Mechanism of spermidine uptake in cultured mammalian cells and its inhibition by some polyamine analogues.

Transport pathways for spermidine (Spd) were characterized in mammalian cells in culture of different origin, i.e. L 1210, P 388, C 6, U 251, Balb/c 3T3 normal and transformed by virus SV40 (SV40/3T3). The kinetic constants (Km and Vmax) for 14C-Spd uptake were found to be different in these cells. Spd uptake was inhibited by spermine and putrescine in all cells. Preloading of these cells with system A and other amino acids, including ornithine, usually did not affect Spd uptake, except in L 1210 and C 6 cells, where Spd uptake was accelerated by 2-aminoisobutyric acid, demonstrating that in these two cell lines the polyamines share the system A pathway. Iso-osmotic replacement of Na+ by choline chloride in the assay medium resulted in a decrease in Spd uptake which suggests that Spd uptake is Na+ activated. In all cells, Spd uptake was inhibited by gramicidin and the Ca2+ ionophore A 23187. The degree of inhibition varied among the cells. Valinomycin (K+ ionophore) inhibited Spd uptake by C 6, P 388, Balb/c 3T3 and SV40/3T3 but not by L 1210 and U 251 cells. Treatment with N-ethylmaleimide or p-L 1210, C 6, Balb/c 3T3 and SV40/3T3 cells did not affect appreciably the uptake process. Some newly synthesized polyamine analogues inhibited the Spd uptake of all cells.

Amino Acids↗
PubMed1990

Polyamine metabolism.

Currently, two major pathways are distinguished along which the polyamines are metabolized: the interconversion pathway and the so-called terminal polyamine catabolism. In vertebrates, the interconversion pathway is a cyclic process which controls polyamine turnover. In conjunction with polyamine transport, it regulates intracellular polyamine homeostasis. In vertebrates, putrescine, the precursor of spermidine and spermine, is exclusively formed by decarboxylation of ornithine--as far as de novo synthesis is concerned. Spermidine and spermine synthase form spermidine from putrescine, and spermine from spermidine, by transfer of aminopropyl residues from decarboxylated S-adenosylmethionine. In the catabolic branch of the interconversion cycle, spermine is degraded to spermidine, and spermidine to putrescine. The first step in this sequence is acetylation in the N1 position. This is followed by oxidative splitting of the acetylated polyamines, whereby the aminopropyl residues which originated from decarboxylated S-adenosylmethionine are removed. The enzyme catalyzing this step is an FAD-dependent oxidase (polyamine oxidase). Ornithine decarboxylase, S-adenosylmethionine decarboxylase, and acetyl CoA:polyamine N1-acetyltransferase are highly regulated, inducible enzymes with a high turnover rate. Depending on the physiological situation, each of these enzymes may become rate limiting. Terminal polyamine catabolism is catalyzed by Cu2(+)-dependent amine oxidases, of which only diamine oxidase has been well defined. By oxidative deamination of a primary amino group, each intermediate of the interconversion cycle can be transformed into an aldehyde, which is further oxidized to an amino acid or a gamma-lactam. The products of the terminal catabolism as well as the acetylated polyamines are urinary excretory products. In addition to intracellularly synthesized polyamines, polyamines from various tissues and from exogenous sources (such as the gastrointestinal tract) may be utilized by those tissues which have a high demand. Polyamines play a paramount role in growth processes. In order to control growth (for example of tumors), it is necessary to block all major polyamine sources. If only one source is blocked, the remaining sources are usually capable of furnishing sufficient polyamines to support growth processes.

Acetylation↗
PubMed1989

Activation of rat liver S-adenosylmethionine decarboxylase by putrescine and 2-substituted 1,4-butanediamines.

1. The activation of S-adenosyl-L-methionine decarboxylase (SAM-DC) by putrescine and a series of 1,4-butanediamines with a substituent in position 2 was studied. 2. Kinetic data show the activation of SAM-DC by putrescine is essentially uncompetitive. 3. All 2-substituted 1,4-butanediamines were activators, although not as potent as putrescine itself. 4. At high concentrations of SAM activation of SAM-DC by putrescine and putrescine analogs deviated considerably from uncompetitive activation kinetics. 5. In order to explain the experimental data, especially the non-linearity of the "fractional velocity plots", it was necessary to postulate two independent, but equivalent activator binding sites, for which substrate (SAM) and activator compete. 6. Based on this kinetic model an equation was derived which describes the rate of SAM decarboxylation as a function of substrate and activator concentrations. 7. From the simulated curves, approximate values for equilibrium constants for the binding of activator and substrate to the activator binding sites, and relative rate constants for the product forming steps were calculated. 8. Even a minor change of the structure, such as the substitution of one hydrogen atom by fluorine in the 2-position of putrescine had a very considerable effect on the potency of activation. 9. It is apparent that the structural requirements of an activator of SAM-DC are highly specific.

Adenosylmethionine Decarboxylase↗
PubMed1989

Ornithine aminotransferase activity, tissue ornithine concentrations and polyamine metabolism.

1. Inactivation of L-ornithine:2-oxoacid aminotransferase (OAT) by 5-fluoromethylornithine (5FMOrn), a specific inactivator of OAT, causes a great elevation of tissue ornithine (Orn) concentrations. 2. Inhibition of L-ornithine decarboxylase (ODC) by 2-difluoromethylornithine (DFMO) had no effect on Orn concentrations. 3. The combined administration of 5FMOrn and DFMO produced a 2- to 3-fold greater enhancement of tissue Orn concentrations than treatment with 5FMOrn alone. 4. The increase of tissue Orn concentrations had a long-lasting enhancing effect on polyamine metabolism. 5. In the brain this could be demonstrated by the elevation of putrescine and spermidine concentrations and the increase of spermidine turnover rate. 6. In visceral organs polyamine concentrations were not elevated because polyamines can be eliminated by transport. 7. In line with this notion is the fact that urinary polyamine excretion was increased for several days, even after a single dose of 5FMOrn. 8. Inhibitors of 4-aminobutyric acid:2-oxoglutarate aminotransferase which are also inactivators of OAT had the same effect on polyamine excretion as 5FMOrn.

Animals↗