Biomedical subjects

B Knödgen

Publications and source records attributed to B Knödgen.

At least 19 recordsLinked to original sources

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

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

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↗

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

(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↗

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

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↗

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↗

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↗

PubMed1985

The influence of catabolic reactions on polyamine excretion.

Complete inhibition of polyamine catabolism is possible by combined administration of two compounds. Aminoguanidine (25 mg/kg body wt., intraperitoneally) inhibits all reactions that are catalysed by copper-containing amine oxidases (CuAO). The products of the CuAO-catalysed reactions cannot be reconverted into polyamines (terminal catabolism) and therefore usually escape observation. N1-Methyl-N2-(buta-2,3-dienyl)butane-1,4-diamine (MDL 72521) is a new inhibitor of polyamine oxidase. It inhibits completely the degradation of N1-acetylspermidine and N1-acetylspermine. The enhanced excretion of N1-acetylspermidine in urine after administration of 20 mg of MDL 72521/day per kg body wt. is a measure of the rate of spermidine degradation in vivo to putrescine, and thus of the quantitative significance of the interconversion pathway. From the enhancement of total polyamine excretion by aminoguanidine-treated rats, one can calculate that only about 40% of the polyamines that are destined for elimination are usually observed in the urine, the other 60% being catabolized along the CuAO-catalysed pathways. The normally observed urinary polyamine pattern gives, therefore, an unsatisfactory picture of the actual polyamine elimination. Although aminoguanidine alone is sufficient to block terminal polyamine catabolism, rats that were treated with a combination of aminoguanidine and MDL 72521 excrete more polyamines than those that received aminoguanidine alone. The reason is that a certain proportion of putrescine, which is formed by degradation of spermidine, is normally reutilized for polyamine biosynthesis. In MDL 72521-treated animals this proportion appears in the urine in the form of N1-acetylspermidine. Thus it is possible to determine polyamine interconversion and re-utilization in vivo and to establish a polyamine balance in intact rats by using specific inhibitors of the CuAO and of polyamine oxidase.

Animals↗

PubMed1983

N-(3-aminopropyl)pyrrolidin-2-one: a physiological excretory product deriving from spermidine.

Normal human and rat urine contain N-(3-aminopropyl)pyrrolidin-2-one. This compound was identified by its chromatographic behaviour on a reversed phase column, by thin-layer chromatography of its dansyl derivative, and by mass spectrometry. Evidence for the presence of conjugates of N-(3-aminopropyl)pyrrolidin-2-one in urine was obtained by the fact that partial acid hydrolysis increases the amount of this compound, whereas prolonged hydrolysis leads to its transformation into isoputreanine (N1-(3-carboxypropyl)-1,3-diamino-propane). Although it is likely that the monoacetylderivative of N-(3-aminopropyl)pyrrolidin-2-one is prominent among the conjugates, since this compound can be formed from N1-acetylspermidine, other types of conjugates are also likely. A method is reported suitable for the measurement of N-(3-aminopropyl)pyrrolidin-2-one and of isoputreanine in urine and urine hydrolysates, respectively. Administration of spermidine enhances the amount of urinary excretion of N-(3-aminopropyl)pyrrolidin-2-one. Of 0.1 mmol . kg-1 of spermidine administered intraperitoneally to rats around 12% are transformed into this compound and its conjugates. Treatment of rats with aminoguanidine sulfate, an inhibitor of diamine oxidase, causes a decrease in the excretion of N-(3-aminopropyl)pyrrolidin-2-one and its derivatives. These findings are in agreement with the assumption that N-(3-aminopropyl)pyrrolidin-2-one, the gamma-lactam of isoputreanine, is a physiological degradation product of spermidine. Its formation is catalyzed by an aminoguanidine sensitive, diamine oxidase-like enzyme.

Animals↗

PubMed1982

N-(3-aminopropyl)pyrrolidin-2-one, a product of spermidine catabolism in vivo.

A high-pressure-liquid-chromatographic method suitable for the separation and sensitive detection of putreanine and isoputreanine is described. This method allowed us to study the formation of the metabolites of the oxidative deamination of spermidine and N1-acetylspermidine. Administration of spermidine trishydrochloride to mice causes a time-dependent accumulation of putreanine and N-(3-aminopropyl)pyrrolidin-2-one in various organs. The latter compound yields isoputreanine by hydrolysis. It can be assumed that the analogous lactam. N-(3-acetamidopropyl)pyrrolidin-2-one is formed from N1-acetylspermidine, since hydrolysis of tissue extracts of N1-acetylspermidine-treated mice produced isoputreanine. No putreanine is formed under these conditions. Pretreatment of the animals with 25 mg of aminoguanidine sulphate/kg body wt. completely inhibits the formation of putreanine and of the respective isoputreanine precursor from spermidine and N1-acetylspermidine. This suggests a role for a diamine oxidase-like enzyme in the oxidative deamination of spermidine and N1-acetylspermidine.

Amino Acids, Diamino↗

PubMed1981

On the formation of amino acids deriving from spermidine and spermine.

Evidence obtained from experiments with rats and mice is presented suggesting that the naturally occurring amino acids putreanine and N8-(2-carboxyethyl)spermidine, and most probably also related compounds deriving from the polyamines spermidine and spermine by oxidative metabolism, are formed within two anatomical compartments. In the first step polyamines are converted into aldehydes by serum spermine oxidase in the circulation. A certain portion of these aldehydes can be taken up by liver and other organs and transformed by aldehyde dehydrogenase into the corresponding amino acids. Putreanine is not only derived from spermidine, but can also be formed from N8-(2-carboxyethyl)spermidine by oxidative deamination, catalysed by serum spermine oxidase, and subsequent spontaneous elimination of acrolein.

Amino Acids↗

PubMed1981

The determination of N1-acetylspermine in mouse liver.

N1-Acetylspermine has been postulated to be an intermediate in the conversion of spermine to spermidine. This compound, together with N1-acetylspermidine has now been detected in the liver of mice which were pretreated with tetrachloromethane. The following methods were used for the identification of N1-acetylspermine: (a) High-pressure liquid-chromatography of the non-derivatized amines on a reversed-phase column, using octane sulfonate for ion-pairing. (b) Thin-layer chromatography of the dansyl derivatives. (c) Mass spectrometry of the dansyl derivatives. Both chromatographic methods allowed the quantitative estimation of N1-acetylspermine and N1-acetylspermidine in the liver of tetrachloromethane-treated animals.

Animals↗