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S Sarhan

Publications and source records attributed to S Sarhan.

At least 37 records · Page 2Linked to original sources
PubMed1988

Chain-fluorinated polyamines as tumor markers--IV. Comparison of 2-fluoroputrescine and 2,2-difluoroputrescine as substrates of spermidine synthase in vitro and in vivo.

1. 2-Fluoroputrescine has a high affinity for spermidine synthase (Km 12 microM) and obeys normal Michaelis-Menten kinetics. 2. The only product of the spermidine synthase-catalysed aminopropylation of 2-fluoroputrescine is 6-fluorospermidine. Formation of the isomeric 7-fluorospermidine could not be detected. 3. 2,2-Difluoroputrescine has even a higher affinity for spermidine synthase than putrescine and 2-fluoroputrescine; however, at concentrations greater than 25 microM one observes inhibition of the aminopropylation reaction. 4. Competition experiments between putrescine and 2,2-difluoroputrescine revealed mixed type inhibition. 5. HTC cells in suspension culture incorporated only small amounts of 2-fluoroputrescine, and even less in the case of 2,2-difluoroputrescine, if they were exposed to 10 microM concentrations of these diamines for up to 24 hr. However, in the presence of 0.5 mM DFMO, a concentration not sufficient to decrease cell growth significantly, but sufficient to decrease cellular putrescine and spermidine concentrations, the uptake of the chain-fluorinated diamines and their transformation into the fluorinated polyamine analogues was dramatically enhanced. In comparison with the difluoro analogues the accumulation rate of monofluoropolyamines was greater by a factor of about two. 6. 6-Fluorospermidine and 6-fluorospermine could be detected in significant quantities in nearly all tissues of mice 48 hr after a single dose (500 mg/kg) of 2-fluoroputrescine. In an analogous experiment with 2,2-difluoroputrescine, the formation of chain-fluorinated polyamines was considerably smaller. 7. Pretreatment of Lewis lung carcinoma bearing C57BL mice with alpha-difluoromethylornithine enhanced the incorporation of 2-fluoroputrescine into all organs, except the brain. Tumor and small intestines showed by far the highest accumulation of 6-fluoropolyamines. 8. Under identical experimental conditions the accumulation of chain-fluorinated polyamines in tumor tissue was more than twice as high with 2-fluoroputrescine as precursor than with the same dose of 2,2-difluoroputrescine. In normal tissues the difference between the uptake of 2-fluoroputrescine and 2,2-difluoroputrescine was usually even greater. 9. From the fact that the accumulation of 6-fluoropolyamines is less selective in tumors than that of 6,6-difluoropolyamines, and from the lower detection sensitivity due to its lower fluorine content, we conclude that 2,2-difluoroputrescine is more advantageous as a tumor marker than 2-fluoroputrescine for detection with 19F-NMR spectroscopy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Synapse formation and development of neurotransmitter functions in neuronal cells from chick brain cultured in a serum-free, defined medium.

Cells dissociated from cerebral hemispheres of 8-day-old chick embryos were seeded on poly-L-lysine coated Petri dishes in serum-containing medium. After 24 hr the culture medium was switched to a serum-free, chemically defined medium. These cultures contain mainly neuronal cells until day 14, characterized by the presence of acetylcholinesterase activity and neurofilament proteins. After 2 weeks glial cells progressively contaminated the neuronal culture. Cultures were maintained for a period of 4 weeks. From day 6 on numerous synapses with clear vesicles were observed. The activity of choline acetyltransferase remained low throughout the culture period, while GABA levels increased in parallel with synaptogenesis. Our observations indicate that chick cerebral hemisphere neuronal cultures grown in serum-free, chemically defined medium contain GABAergic neurons that undergo maturation.

Animals↗
PubMed1987

Chain-fluorinated polyamines as tumor markers--I. In vivo transformation of 2,2-difluoroputrescine into 6,6-difluorospermidine and 6,6-difluorospermine.

1. Injection of 2,2-difluoroputrescine (DFPut) into the yolk sac of chick embryos causes the formation of 6,6-difluorospermidine (6,6DFSpd) and 6,6-difluorospermine (6,6DFSpm), demonstrating that the difluoroanalogs of putrescine and spermidine are in vivo substrates of spermidine and spermine synthase, respectively. 2. Depletion of tissue putrescine and spermidine concentrations by administration of D,L-alpha-difluoromethylornithine (DFMO, Ornidyl) causes a very marked enhancement of difluoropolyamine formation from DFPut. 3. The major accumulation of 6,6DFSpd and 6,6DFSpm in DFMO-pretreated rodents occurs in small intestines and tumors, i.e. in tissues with high cell proliferation rates, which are also the most susceptible to polyamine depletion by inhibition of ornithine decarboxylase. 4. Their preferential accumulation in tumors and the fact that DFPut and its metabolites seem not to exert toxic effects, suggest DFPut as a serious candidate for the use as probe in 19F-NMR imaging of tissues with a high proliferation rate and a high rate of polyamine biosynthesis.

Animals↗
PubMed1987

Putrescine derivatives as substrates of spermidine synthase.

1. Derivatives of 1,4-butanediamine (putrescine) were studied in vitro and in vivo as potential substrates of spermidine synthase. 2. Substituents in the 1-position decreased the reaction rate by steric hindrance, and in the case of electron withdrawing groups there was an additional decrease due to the lowered basicity of the vicinal amino group. 3. Substituents in the 2-position are tolerated; under saturating conditions reaction rates are comparable to those of putrescine. 4. Compounds which were identified as substrates of spermidine synthase in vitro formed derivatives of spermidine and spermine in vivo. Exception: compounds, such as 1-methylputrescine formed in vivo only a spermidine derivative, because the second aminopropylation was sterically hindered by the substituent on the carbon atom next to the amino group. 5. Administration of 2-hydroxyputrescine to alpha-difluoromethylornithine-pretreated chick embryos produced spermidine and spermine analogues in amounts exceeding spermidine and spermine formation from putrescine under comparable conditions. 6. Since the concentration of 2-hydroxyputrescine in the embryo was higher than that of putrescine and all other putrescine analogues, it appears that uptake of the polyamine precursor from the yolk may be rate limiting. 7. Three days after administration of 5 mM alpha-difluoromethylornithine there is a near-to-complete arrest of embryonal growth. 8. A series of diamines supported growth under these conditions, even if they were not substrates of spermidine synthase. 9. Survival of chick embryos was, however, only supported if the diamines were capable of forming significant amounts of spermidine and spermine analogues.

Animals↗
PubMed1985

Amplification by glycine of the anticonvulsant effect of THPO, a GABA uptake inhibitor.

THPO, a GABA uptake inhibitor, when given in doses of up to 4 mmol/kg (i.p.) to mice, had only a marginal protective effect against seizures induced 1 hr later by 3-mercaptopropionic acid (MPA). THPO (4 mmol/kg), when given in combination with 10 mmol/kg of glycine, protected 60% of the mice from MPA-induced convulsions. The combination of THPO and glycine delayed the onset of metrazol-induced clonic convulsions and protected 30% of the animals from seizures, although neither glycine or THPO alone had a significant anticonvulsant effect against metrazol induced seizures. In agreement with earlier findings, the results presented in this work seem to indicate that the synergistic anticonvulsant effects of glycine and GABAergic agents are independent of their mode of action: the effects of GABA agonists (muscimol) GABA-T inhibitors (vinylGABA), or an inhibitor of glial GABA uptake (THPO) are similarly amplified by glycine.

3-Mercaptopropionic Acid↗
PubMed1984

Synergistic anticonvulsant effects of GABA-T inhibitors and glycine.

The anticonvulsant effect of inhibitors of GABA-T (R/S-gamma-vinyl-GABA, ethanolamine-O-sulfate, gabaculine, aminooxyacetic acid) was enhanced by 10 mmol/kg glycine in animal seizure models which are based on a functional GABA deficit. Similar to glycine in their action, although less effective, were its close structural analogues (sarcosine, N,N-dimethylglycine) and homologous omega-aminoacids (beta-alanine, taurine, gamma-aminobutyric acid, delta-aminovaleric acid). It is assumed that glycine and its structural analogues act on supraspinal glycine receptors as glycine agonists. Our observation is the first example of the synergistic interaction of two inhibitory neuronal systems resulting in the amplification of the anticonvulsant effect. Combined treatment with GABA-T inhibitors and glycine may turn out to be of practical importance in the therapy of seizure disorders and other diseases, for which treatment with GABA-T inhibitors is considered a potentially useful therapeutic approach.

3-Mercaptopropionic Acid↗
PubMed1984

Polyamines and the development of isolated neurons in cell culture.

The possible role of polyamines in the development of isolated neuroblasts from the cerebral cortex of embryonic chick brain was studied by means of three enzyme activated irreversible inhibitors of ornithine decarboxylase. alpha-Difluoromethylornithine (MDL 71782) showed no effects on development at doses which depleted dramatically neuronal putrescine and spermidine levels. In contrast, the two other inhibitors, (E)-alpha-(fluoromethyl)dehydroputrescine (MDL 72197) and 6-heptyne-2,5-diamine (MDL 72175) blocked the formation of neuronal outgrowths completely at 100 microM and higher concentrations. Their effects on neuronal polyamines differed at this concentration considerably. The growth inhibitory effect of the ornithine decarboxylase inhibitors was in all cases reversible: cells which were grown after 3 days of exposure to the drugs in normal medium produced neuronal networks. The presence of putrescine at 10 microM concentration in the culture medium prevented the growth inhibitory effect of 100 microM concentrations of the drugs. This concentration of putrescine was not only capable of preventing, but also of reversing growth inhibition by the ornithine decarboxylase inhibitors. Although the cellular polyamine levels were not correlated with the morphological development of chick embryo cortical neurons, the present study leaves no doubt that putrescine plays an essential role in neuronal differentiation.

Alkynes↗
PubMed1984

Synergistic anticonvulsant effects of a GABA agonist and glycine.

Administration of muscimol to mice in subcutaneous doses between 0.34 and 1.25 mg/kg produced partial protection against 3-mercaptopropionic acid (MPA)-induced seizures. Glycine at a dose of 750 mg/kg (10 mmol/kg) protected 20% of the animals 45 min after its administration. Combined treatment with the two compounds gave a near to complete protection against MPA-induced seizures. These observations suggest that the concomitant enhancement of glycinergic and GABAergic activities amplify the anticonvulsant effect of these neuronal systems against seizures induced by impairment of GABA-mediated transmission.

3-Mercaptopropionic Acid↗
PubMed1984

The amplification of the anticonvulsant effect of vinyl GABA (4-aminohexenoic acid) by esters of glycine.

The synergistic amplification of the anticonvulsant effects of direct and indirect GABA agonists by glycine has previously been demonstrated. We show in the present report that the anticonvulsant effect of vinyl GABA, a GABA-T (4-aminobutyrate: 2-oxoglutarate aminotransferase) inhibitor with antiepileptic efficacy, can be amplified by esters of glycine. Among the compounds studied glycine tert. butylester was the most promising. It was effective at a lower dose and had a considerably longer duration of action than glycine. From the observed glycine and glycine tert. butylester levels it is evident that glycine tert. butylester is rapidly hydrolysed within brain and other tissues. It is therefore a pro-drug of glycine, capable of enhancing central glycinergic activity.

3-Mercaptopropionic Acid↗
PubMed1983

Anticonvulsant effects of some inhibitory neurotransmitter amino acids.

The anticonvulsive effects of GABA, taurine, and glycine were investigated on several chemically-induced and genetic seizure models. Intravenous injections of either GABA, taurine, or glycine provided protection against 3-mercaptopropionic acid (MPA)-induced convulsions in adult Swiss mice. GABA was partially effective against isonicotinic acid hydrazide and was without effect against bicuculline-induced convulsions. Prolonged administration of glycine prevented MPA-induced convulsions but not electrically induced seizures or seizures induced by strychnine or metrazol. Intragastric glycine protected young audiogenic seizure-susceptible DBA/2 mice against all three phases of sound-induced convulsions (wild running, clonic and tonic seizure), but GABA and taurine provided little or no protection. With increase of glycine, the cerebral levels of glutamine and serine also increased, but that of glutamic acid decreased. The endogenous glutamic and glycine levels were slightly higher in the brains of the audiogenic seizure-susceptible DBA/2 mice than in that of the resistant BALB/Cy strain.

Acoustic Stimulation↗
PubMed1981

Developmental changes of the GABA and polyamine systems in isolated neurons in cell culture.

Dissociated cells of cerebral hemispheres from 8-day-old chick embryos were cultivated for 8 days in polylysine-coated Petri dishes. Changes of DNA, RNA, total proteins, putrescine, spermidine, spermine, free amino acids and enzymes involved in polyamine and GABA metabolism were studied throughout neuronal development in culture. The presence of GABAergic neurons in the cultured cell population was demonstrated. There were time-dependent changes in cellular polyamine concentrations and the activities of the enzymes involved in polyamine metabolism. Since no significant proliferation took place after the first day in culture, the observed changes indicate a role of polyamine metabolism during neuronal differentiation; it was not possible, however, to attribute the observed changes to specific functions. This culture system seems especially useful for the study of biochemical and of functional correlations between GABA and polyamine metabolism and morphological and functional developments of neurons.

Aging↗
PubMed1980

Drugs affecting GABA.

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4-Aminobutyrate Transaminase↗
PubMed1979

Rapid method for the assay of 4-aminobutyric acid (GABA), glutamic acid and aspartic acid in brain tissue and subcellular fractions.

The thin-layer electrophoretic separation at pH 4.8 of brain extracts and a procedure for fluorescent staining of the plates with fluorescamine are described for the rapid routine determination of 4-aminobutyric acid (GABA), glutamic acid and aspartic acid in brain extracts and in particulate fractions of brain tissue. Automated sample application, electrophoretic separation using two chambers, and quantitation by in situ fluorescence scanning allows the assay of 280 samples within three working days. The method is reproducible (S.D. less than 8% of the mean) within the range of 0.2--2 nmole per spot. The staining procedure can be applied to a variety of related analytical problems. The method has proved useful for the determination of the specific radioactivities of GABA, glutamic acid and aspartic acid in metabolic studies.

Aging↗
PubMed1979

Metabolic inhibitors and subcellular distribution of GABA.

Experimental procedures are described which are believed to yield results that reflect, within certain limits, the in vivo changes of the size of the GABA pool in nerve endings in comparison with those of all other GABA pools. Two irreversible GABA-T inhibitors, vinyl GABA and acetylenic GABA, two GAD inhibitors, 3-mercaptopropionic acid and pyridoxal phosphate glutamyl-gamma-hydrazone, and di-n propylacetate, a clinically useful anticonvulsant, have been studied to determine their effects on GABA compartmentalization in mouse brain cortex. The changes elicited by these drugs in subcellular fractions of brain cortex homogenates support the notion that measurement of amino acid concentrations in crude synaptosomal fractions and in supernatant fractions under controlled conditions allow one to draw conclusions about relative changes of pool sizes in vivo. In particular this work showed that a specific increase in the concentration of GABA within the nerve endings is more important than a large increase of total brain GABA as a means of decreasing susceptibility to a variety of chemically or physically induced seizures.

3-Mercaptopropionic Acid↗
PubMed1979

On the formation of gamma-aminobutyric acid from putrescine in brain.

Gamma-aminobutyric acid is not formed in significant amounts from putrescine by incubation with rat brain homogenates. However, it is formed if acetyl-CoA is added to the incubation medium. This is taken as further evidence for the existence of a metabolic pathway in mammalian brain which comprises acetylation of putrescine to monoacetyl putrescine and oxidative deamination of monoacetyl putrescine by MAO. Nerve cells and glia cells have comparable capacities for putrescine degradation along this pathway.

Acetyl Coenzyme A↗
PubMedDate not supplied

Polyamine deprivation, malnutrition and tumor growth.

Feeding an artificial, essentially polyamine-free diet which contained antibiotics for the decontamination of the gastrointestinal tract and 2-(difluoromethyl)ornithine (DFMO) and N,N'-bis-(2,3-butadienyl)putrescine for the inactivation of ornithine decarboxylase and polyamine oxidase, respectively, retarded the growth of several solid tumors by about 80%. In the present work the contribution of the major components of the treatment were analysed, using Lewis lung carcinoma growing in the hind leg of female C57BL mice. In addition to polyamine deprivation, malnutrition due to decreased food intake turned out to contribute significantly to tumor growth retardation. Ornithine decarboxylase was shown to be incompletely inhibited by administration of DFMO with the diet. A considerable improvement of polyamine deprivation can be expected from the continuous administration of this drug, or from analogous inhibitors with more favourable enzyme- and pharmaco-kinetic properties.

Animals↗