Biomedical subjects

S Sarhan

Publications and source records attributed to S Sarhan.

At least 19 recordsLinked to original sources

PubMed1997

Comparative antipsychotic profiles of neurotensin and a related systemically active peptide agonist.

Several lines of evidence have shown that neurotensin can modulate dopamine neurotransmission. It has been suggested that neurotensin has potential antipsychotic activity because it reduces dopaminergic activity preferentially in the nucleus accumbens. In the present study, the effects of neurotensin and NT1 (N alpha Me-Arg-Lys-Pro-Trp-TIe-Leu or Eisai hexapeptide), a metabolically stable and systemically active neurotensin agonist, were examined in several models of antipsychotic activity and side effect liability in mice; analgesic and hypothermic effects of both compounds also were determined. Up to high doses, neurotensin (5.0 and 10.0 micrograms, i.c.v.) and NT1 (10.0 and 20.0 mg/kg, i.p.) did not produce catalepsy. A much lower dose of neurotensin (0.03 microgram, i.c.v.) significantly reduced amphetamine- and phencyclidine-stimulated locomotor activity; NT1 also diminished amphetamine- and phencyclidine-stimulated locomotion with ED50 values of 0.3 and 0.4 mg/kg, i.p., respectively. Neurotensin (0.01-0.3 microgram, i.c.v.) and NT1 (0.1-1.0 mg/kg, s.c.) also produced dose-dependent analgesia in the paw pressure test and decreased body temperature; these effects were insensitive to pretreatment with naloxone (10.0 mg/kg, i.p.). Together, the results support the hypothesis that neurotensin agonists have antipsychotic and analgesic activity. Moreover, the data suggest that such compounds may not produce extrapyramidal side effects.

Analgesics↗

PubMed1995

Suppression of haloperidol-induced oral dyskinesias in rats by vigabatrin.

Acute and chronic administration of vigabatrin, a selective inactivator of GABA-T, suppresses haloperidol-induced dyskinesias at low doses without preventing the enhancement of striatal dopamine D2 receptor density or the development of vacuous chewing movements. The long-term administration of vigabatrin does not attenuate its effect. The observations presented in this work support the GABA hypothesis of haloperidol-induced vacuous chewing behavior in rats, and suggest that vigabatrin is an appropriate means to enhance nigral GABAergic activity.

4-Aminobutyrate Transaminase↗

PubMed1994

Determination of orotic acid in urine.

Orotic acid was separated from other urinary constituents by ion-pair formation with tetrabutylammonium, and isocratic elution from a reversed-phase column. Absorbance at 280 nm was recorded for quantitation. Owing to the better column characteristics the separations are somewhat faster, and the sensitivity of the method is higher than those of analogous methods using anion-exchange columns. The method was used for the determination of orotic acid in human urine, in urine of rats with portacaval shunts and in small (30 microliters) urine samples from sparse fur mice. Shunted rats excreted ca. 100% more orotic acid per 24 h than sham-operated controls, in spite of their considerably lower body weight. Excessive orotic acid in urine indicates a conditional deficiency of ornithine. Sparse fur mice are congenitally hyperammonemic because of a defective hepatic ornithine carbamoyltransferase. Determination of orotic acid in the urine is a suitable method to identify those animals among litter mates which have the hereditary enzyme defect.

Animals↗

PubMed1994

Decreased hyperammonaemia and orotic aciduria due to inactivation of ornithine aminotransferase in mice with a hereditary abnormal ornithine carbamoyltransferase.

Mice with the X-chromosomal sparse-fur (spf) mutation are an animal model of some hereditary deficiencies of ornithine carbamoyltransferase (OCT) in man. Orotic aciduria and hyperammonaemia are the most conspicuous metabolic changes in these diseases. Selective inactivation of ornithine aminotransferase (OAT) by 5-fluoromethylornithine raises endogenous ornithine concentrations so that citrulline formation is effectively catalysed by the aberrant OCT, in spite of its low affinity for ornithine. As a consequence, blood and tissue ammonia concentrations and orotic acid excretion are reduced near to normal values, and the abnormal amino acid patterns in blood, brain and liver are normalized. Selective inactivation of OAT seems a promising therapeutic approach in some hereditary OCT deficiencies, and a total that may allow us to clarify the role of ammonia and orotic acid in the development of nanism and abnormal behaviour in spf mutant mice.

Amino Acids↗

PubMed1994

Effects of ornithine aminotransferase inactivation by 5-fluoromethylornithine in rats following portacaval anastomosis.

5-Fluoromethylornithine (5FMOrn) is a selective inactivator of ornithine aminotransferase. Administration of this compound to rodents causes a prominent increase of tissue ornithine concentrations, and prevents the neurological consequences of acute ammonia intoxication. However, long-term treatment with 5FMOrn of rats with portacaval shunts did not result in decreased circulating ammonia concentrations, nor did it prevent other pathologic manifestations of shunting. The sensitivity to ammonia intoxication of rats with portacaval shunts was also unaffected by pretreatment with 5FMOrn, although liver ornithine concentrations were significantly elevated; specific activities of urea cycle enzymes were slightly higher in portacaval shunted compared to sham-operated controls following 5-FMOrn treatment. Administration of 5FMOrn dramatically elevated urinary excretion of several amino acids in rats with portacaval shunts, but not in sham-operated animals, suggesting that the reabsorption of amino acids from the glomerular filtrate may be impaired in shunted rats. These results suggest that, in contrast to acute hyperammonemic syndromes, 5-FMOrn may be of limited therapeutic value in chronic hyperammonemia syndromes in which there is significant portal-systemic shunting.

Amino Acids↗

PubMed1994

Protection against lethal ammonia intoxication: synergism between endogenous ornithine and L-carnitine.

The protective effects of combinations of 5-fluoromethylornithine (5FMOrn), a selective inhibitor of ornithine aminotransferase, and of compounds known to antagonize ammonia toxicity, were studied in acute, lethal ammonia intoxication in mice. Two test conditions were used: (a) Mice were pretreated with 5FMOrn at a dose (5 mumol.kg-1) which partially protects against 13 mmol.kg-1 ammonium acetate. (b) Mice were pretreated with a maximally protective dose of 5FMOrn (0.1 mmol.kg-1), however, 15 mmol.kg-1 ammonium acetate was used for intoxication. Under these conditions treatment with 5FMOrn alone protected only marginally. Under condition (a), administration of L-citrulline, L-carnitine, and L-acetylcarnitine improved the protective effect of 5FMOrn significantly, in an additive manner. N-acetyl-L-glutamate administration was ineffective. Under condition (b), ornithine, arginine and citrulline did not improve the protective effect of 5FMOrn, even when these amino acids were given at doses, which were effective in preventing ammonia toxicity induced with 13 mmol.kg-1 ammonium acetate. The inability to improve the effect of 5FMOrn by these compounds is most probably due to the fact that 5FMOrn and these amino acids enhance urea formation by the same mechanism, namely by increasing the concentration of substrates of the urea cycle. In contrast, L-carnitine and L-acetylcarnitine, which are assumed to stimulate urea production by different mechanisms, or compounds which antagonize ammonia toxicity by a urea cycle-independent mechanism, such as antagonists of the NMDA-type glutamate receptor (MK-801; MDL 100,453), potentiated the effects of 5FMOrn. The principle reason for the observed protective effects of the treatments described in this work seems to be the prevention of accumulation of lethal concentrations of ammonia in the brain. But other effects may also contribute.

Acetates↗

PubMed1994

Effect of ammonia on endocytosis, cytokine production and lysosomal enzyme activity of a microglial cell line.

Ammonia is a natural lysosomotropic compound. Concentrations of ammonium acetate > 2 mM impaired the phagocytic activity of BV-2 cells, an immortalized microglial cell line, as was determined by the uptake of fluorescent latex microspheres of different sizes. In contrast, an increase in the uptake of fluorescent dextran was observed with the elevation in ammonium acetate concentrations. This indicates that ammonia affects phagocytotic and pinocytotic activities of BV-2 cells differently. Interferon-gamma- and polyinosinic-polycytidylic acid-stimulated secretion of IL1 alpha as well as LPS-stimulated secretion of IL6 decreased with an elevation in ammonium acetate concentrations. The constitutive secretion of IL1 alpha was not significantly affected by ammonium acetate. However, an increase in LPS-stimulated IL1 alpha secretion was observed at 10 mM and 20 mM ammonium acetate. High concentrations of ammonia affected the activity of lysosomal enzymes of the BV-2 cells. Acid phosphatase and alpha-glucosidase activities increased with the increase in ammonium acetate up to 20 mM. The activity of cathepsin D was increased at 5 mM, but decreased at higher ammonia concentrations. The effects of ammonia on microglial functions are discussed with respect to pathogenetic mechanisms of dementia of the Alzheimer type.

Acetates↗

PubMed1993

Effects of inhibition of ornithine aminotransferase on thioacetamide-induced hepatogenic encephalopathy.

Repeated administration of thioacetamide (TAA) to CD1 mice produced hepatic failure and biochemical and behavioral effects characteristic of hepatogenic encephalopathy (HE). The symptoms in mice resembled those previously observed in rats after similar treatments. It is, however, obvious that both in rats and mice the severity of symptoms depends not only on dose and dosing schedule of TAA, but also on strain and body weight (age). Administration of 5-fluoromethylornithine (5FMOrn), a selective inactivator of ornithine aminotransferase (OAT), significantly reduced mortality, and it ameliorated most of the TAA-induced pathologic symptoms, such as hypothermia, decreased locomotor and exploratory behavior, pathologic liver function and amino acid patterns. The most prominent biochemical consequence of 5FMOrn administration is the elevation of ornithine concentrations in tissues, including the brain, and in body fluids. Elevated ornithine concentrations are, therefore, the most likely basis for the therapeutic effects of 5FMOrn. In agreement with this notion is the enhancement of citrulline and urea formation. These findings and the observation that administration of ornithine in combination with a branched-chain 2-oxoacid ameliorated the pathologic symptoms of portal-systemic encephalopathy suggest inhibition of OAT in the treatment of this disease. The liver protective effect of 5FMOrn is not yet understood; the enhancement of regenerative processes is a likely explanation.

Amino Acids↗

PubMed1993

Enhanced endogenous ornithine concentrations protect against tonic seizures and coma in acute ammonia intoxication.

Pretreatment of mice with 5-fluoromethylornithine (5FMOrn), a selective inactivator of ornithine aminotransferase, diminishes the accumulation of ammonia in the brain after administration of ammonium acetate, and antagonizes ammonia-induced fatal tonic extensor convulsions. In about 50% of the treated animals the loss of the righting reflex and coma is prevented. Presumably these effects are based on the enhancement of urea formation by the increased liver ornithine concentrations. However, since brain ornithine concentrations are greatly enhanced by 5FMOrn, it is not excluded that ornithine has direct effects on cellular events involved in ammonia-induced seizure generation, even though 5FMOrn had no anticonvulsant properties in a series of established animal seizure models, including N-methyl-D,L-aspartate-induced convulsions. NMDA receptor antagonists are capable of preventing death, but do not protect against the generation of coma and tonic extensor convulsions in ammonium acetate intoxicated mice. Since no evidence was found for ammonia-induced glutamate release from rat hippocampus, there is no convincing evidence for the idea that the tonic convulsions are mediated by NMDA receptors. L-Methionine-D, L-sulfoximine (MSO)-induced seizures can be partially antagonized by pretreatment with 5FMOrn. However, the effect is considerably smaller than against ammonia-induced convulsions, although at the time of seizure onset brain ammonia levels of MSO-intoxicated mice were lower than in the animals receiving ammonium acetate. This suggests that MSO-convulsions are not entirely due to the elevation of brain ammonia concentrations, even though MSO administration mimics effects of ammonia on cortical inhibitory neuronal interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Mercaptopropionic Acid↗

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↗

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↗

PubMed1989

Proline and proline derivatives as anticonvulsants.

1. The anticonvulsant properties of L-proline, of proline derivatives (trans-4-hydroxy-L-proline, cis-4-hydroxy-D-proline, 3,4-dehydro-D,L-proline) and of D- and L-pipecolic acid were studied alone and in combination with vigabatrin (R/S-4-aminohex-5-enoic acid). 3-Mercaptopropionic acid and pentylenetetrazol-induced convulsions in mice were used as animal models of epilepsy. 2. Proline and proline derivatives are weak anticonvulsants if given alone in doses up to 10 mmol/kg, however, they are capable of potentiating the anticonvulsant effects of vigabatrin, in a manner similar to that reported previously for glycine, and some glycine derivatives. Among the compounds tested, trans-4-hydroxy-L-proline was the most potent anticonvulsant in combination with the indirect GABA agonist vigabatrin. 3. A potential explanation for the synergistic anticonvulsant effect of the combination of the GABA agonist and proline is the presumed role of proline as inhibitory neurotransmitter, and/or its glutamate antagonistic effects. 4. The current study points out the lack of basic knowledge on the neurochemistry and pharmacology of proline and hydroxyproline.

3-Mercaptopropionic Acid↗

PubMed1989

On the subcellular localization of the polyamines.

Putrescine, spermidine and spermine were determined in the nuclear fraction of rat liver which was obtained by density gradient centrifugation in non-aqueous media, i.e. under conditions which avoid migration of water-soluble compounds. Calculations of the distribution of the polyamines between nuclear and extranuclear compartments were based on the assumption that the DNA is concentrated in the nuclei. No significant losses of the polyamines occurred during fractionation. From the polyamine determination in tissue and nuclear fraction it appeared that 16-17% of the liver spermidine and spermine, and about 8% of the putrescine content was localized in the nuclei. The spermidine/spermine-ratios in nuclei and whole tissue were not significantly different. Pretreatment of the animals with inhibitors of ornithine decarboxylase caused a decrease of putrescine exclusively in the extranuclear compartments, in agreement with a higher proportion of the inhibitors in the cytoplasm. Since the nuclear volume of rat liver corresponds to about 5% of total liver volume, the concentration of spermidine and spermine is higher in the nucleus than in extranuclear compartments. Published histochemical localizations of the polyamines suggested very low polyamine concentrations in the nuclei of non-dividing liver and HeLa cells, but dramatic polyamine accumulations in metaphase and anaphase nuclei. These results are in disagreement with previously reported autoradiographic data, subcellular localizations based on density gradient centrifugations, and with our present results. Since subcellular localization is a key issue in all attempts to clarify cellular functions of the polyamines the careful revision of the techniques involved in subcellular polyamine localizations seems imperative.

Adenosylmethionine Decarboxylase↗

PubMed1988

Chain-fluorinated polyamines as tumor markers. II. Metabolic aspects in normal tissues.

The objective of this work was to study certain metabolic aspects of fluorine-substituted analogues of natural polyamines in healthy experimental animals, with the aim of exploring their potential application as tumor markers. Tissue polyamine concentrations were more effectively depleted by combined treatment with D,L-alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, and N1,N4-bis-allenylputrescine, an inactivator of polyamine oxidase, than with either inhibitor alone. This suggests the general importance of polyamine interconversion as a metabolic source of putrescine. Administration of 2,2-difluoroputrescine after 2 weeks pretreatment with the two inhibitors caused the formation of 6,6-difluorospermidine and 6,6-difluorospermidine in nearly all tissues. Highest concentrations of the chain-fluorinated polyamines were observed in the small intestine. At 24 h after 2,2-difluoroputrescine administration the amount was about 8% of the normal endogenous polyamine pool in the small intestine, but lower in all other tissues. Replenishment of endogenous polyamine pools is a relatively slow process. Approximately 9 days after cessation of treatment with the two inhibitors normal values had been reestablished. The rate of formation of endogenous polyamines was not affected by the presence of their difluoro analogues. Elimination of the chain-fluorinated polyamines from tissues seems not to follow normal polyamine metabolic patterns. Their most rapid elimination coincides with the enhancement of endogenous polyamines, indicating that the fluoro analogues are displaced by the natural polyamines. Most of the 2,2-difluoroputrescine was rapidly excreted in the urine, and formation of a conjugate was detected. 6,6-Difluorospermidine was also a urinary excretion product. However, the metabolic fate of 6,6-difluorospermine could not be clarified. It was not found in urine, either free or as conjugate. The relatively low accumulation of chain-fluorinated polyamines, together with their rapid elimination from normal tissues are characteristics which together with their previously established selective uptake into rapidly proliferating tissues recommend them as potential tumor markers that can be determined by 19F-NMR spectroscopy.

Animals↗