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N Seiler

Publications and source records attributed to N Seiler.

At least 37 records · Page 2Linked to original sources
PubMed1998

Polyamine metabolism as target for cancer chemoprevention (review).

The natural polyamines putrescine, spermidine and spermine are intimately involved in growth-related processes. More and more evidence indicates that the excessive accumulation of putrescine and spermidine favors malignant transformation of cells. Selective depletion of putrescine has been shown to restore in some transformed cells the normal phenotype. Inhibition of polyamine formation appears, therefore, a rational target in chemoprevention. Clinical trials with 2-(difluoromethyl)ornithine, a selective inactivator of ornithine decarboxylase, a key enzyme of polyamine biosynthesis, are promising. Structural analogs of the polyamines with polyamine-mimetic or antagonist properties, and calmodulin antagonists are other types of drugs which affect several key reactions of polyamine metabolism, and appear to be candidates for the prevention of carcinogenesis especially of the gastrointestinal tract.

Antineoplastic Agents↗
PubMed1997

Flow cytometric analysis of in vivo polyamine deprivation in Lewis lung carcinoma (3LL) cells using the monoclonal antibody SPM8-2.

It has previously been shown that the monoclonal antibody SPM8-2 recognizes free spermine and spermidine as well as polyamines bound by an amide bond. In the present work it is demonstrated that this antibody also interacts with spermidine, spermine, and to a lesser extent N1- and N8-acetyl spermidine in an ELISA test where the polyamines are bound by reaction with formaldehyde. 3LL Lewis lung carcinoma cells from tumor-grafted mice were labeled with fluorescein-conjugated monoclonal antibody SPM8-2 and analyzed by flow cytometry. Both viable cells and formaldehyde-fixed and subsequently permeabilized cells showed fluorescent staining. However, most polyamines present in the cells are not directly available for antibody binding. Treatment of fixed cells with DNase or RNase greatly increased fluorescent staining, suggesting that some polyamines are co-localized with DNA and RNA. Antibody labeling of the cells was prevented by addition of free spermine. 3LL cells from tumors of mice treated by a polyamine depleting regimen had decreased intracellular spermidine levels and bound less antibody when compared to untreated controls. After digestion with RNase, the cells from treated mice bound considerably less fluorescent antibody than tumor cells from untreated mice, while their RNA content was similar. In contrast, fluorescent staining after DNase digestion was only slightly affected by the treatment with a polyamine depleting regimen. This suggests that the pools of polyamines which are co-localized with RNA are depleted more readily than those associated with DNA. Since only a small proportion of the intracellular polyamines is accessible to the bulky antibodies, treatment with hydrolytic enzymes (DNase, RNase) is necessary to reveal specific compartments of the polyamines and to demonstrate qualitative and semi-quantitative differences of their distribution within cells.

Animals↗
PubMed1997

N1-dansyl-spermine and N1-(n-octanesulfonyl)-spermine, novel glutamate receptor antagonists: block and permeation of N-methyl-D-aspartate receptors.

The effects of several N-sulfonyl-polyamines, including N1-dansyl-spermine (N1-DnsSpm) and N1-(n-octanesulfonyl)-spermine (N1-OsSpm), were studied at recombinant N-methyl-D-aspartate (NMDA) receptors expressed in Xenopus laevis oocytes. N1-DnsSpm and N1-OsSpm inhibited NMDA receptors and were approximately 1000-fold more potent than spermine in oocytes voltage-clamped at -70 mV. Block by N1-DnsSpm and N1-OsSpm was strongly voltage dependent, being more pronounced at hyperpolarized membrane potentials. With the Woodhull model of voltage-dependent channel block, the values of Kd(0) were 779 microM, 882 microM, and 7.4 mM and those of z delta were 2.58, 2.57, and 1.07 for N1-DnsSpm, N1-OsSpm, and spermine, respectively. This suggests that an increase in the voltage dependence of block together with an increase in affinity contributes to the increased potencies of N1-DnsSpm and N1-OsSpm compared with spermine. Sensitivity to N1-DnsSpm was reduced by mutation NR1(N616Q) and was increased by mutations NR1(N616G) and NR2A(N615G). The NR1(N616G) and NR2A(N615G) mutations decreased the Kd(0) value of N1-DnsSpm without affecting z delta, whereas the NR1(N616Q) mutation reduced z delta. These mutations may alter the accessibility of part of the polyamine binding site within the channel pore or directly alter the properties of that site. Block by N1-DnsSpm (0.3 microM) was almost complete at -100 mV, and there was no relief of block at extreme negative membrane potentials (-100 to -200 mV) at wild-type NR1/NR2A channels. In contrast, block by N1-DnsSpm was partially relieved at extreme negative potentials at receptors containing NR1(N616G) or NR2A(N615G), suggesting that N1-DnsSpm can permeate these mutant channels but not wild-type NR1/NR2A channels. This is hypothesized to be due to an increase in the pore size of channels containing NR1(N616G) or NR2A(N615G), which allows passage of the bulky head group of N1-DnsSpm. In contrast to N1-DnsSpm, N1-OsSpm could easily permeate wild-type NR1/NR2A channels, presumably because the head group of N1-OsSpm can pass through the narrowest part of the channel pore. N-Sulfonyl-polyamines such as N1-DnsSpm and N1-OsSpm represent a new class of polyamine antagonists with which to study glutamate receptor ion channels.

Amino Acid Sequence↗
PubMed1997

Bis(7-amino-4-azaheptyl)dimethylsilane: a new tetramine with polyamine-like features. Effects on cell growth.

Bis(7-amino-4-azaheptyl)dimethylsilane is a new type of aliphatic polycation with structural features resembling those of spermine. The elongation to a seven-membered carbon chain in which the central CH2-group was substituted by (CH3)2Si renders the molecule more lipophilic than spermine. Cells accumulate the compound via the polyamine transport system. Due to suppression of ornithine decarboxylase, de novo putrescine biosynthesis is impaired, and intracellular putrescine and spermidine concentrations are depleted. Depletion of intracellular spermidine together with binding to functionally important polyamine binding sites are considered the main features of the compound which cause cytostatic, and at high concentrations, cytotoxic effects.

Animals↗
PubMed1997

Dimethylsilane polyamines: cytostatic compounds with potentials as anticancer drugs.

Several dimethylsilane tetramines [homologs of spermine with an Si(CH3)2 group in the central carbon chain], a carbon analog of the dimethylsilane tetramines [containing C(CH3)2 instead of Si(CH3)2] and a dimethylsilane hexamine were studied with regard to their cytotoxic activity and their ability to interact with double-stranded DNA. All polyamine analogs exerted cytostatic effects to several cell lines at micromolar concentrations. Their ability to condense DNA was comparable to and their ability to displace ethidium bromide from binding to DNA was superior to that of spermine. Their cytostatic effect was not correlated with the depletion of cellular spermidine concentrations. It is suggested that the new polyamine analogs act mainly by displacing spermidine from binding sites which are essential for the promotion of cell growth.

Animals↗
PubMed1996

Bis(7-amino-4-azaheptyl)dimethlysilane and bis(7-ethylamino-4-azaheptyl)dimethylsilane: inhibition of tumor cell growth in vitro and in vivo.

Bis(7-amino-4-azaheptyl)dimethylsilane (AzhepSi) and its bis(ethyl) derivative [bis(7-ethylamino-4-azaheptyl)dimethylsilane] (EtAzhepSi) are the first examples of a new type of aliphatic tetramine with a dimethylsilane group incorporated into the central carbon chain. AzhepSi shares certain properties with the natural polyamines, but in contrast with spermidine and spermine it inhibits the growth of L1210 leukemia cells in culture at micromolar concentrations. The bis(ethyl) derivative of AzhepSi was made, in analogy to bis(ethyl) spermine, a polyamine derivative, which gained much attention during the last decade as a potential anticancer drug. Chinese hamster ovary (CHO) cells accumulate the dimethylsilyl tetramines considerably more and are more sensitive to these drugs than are CHO-MG cells, a polyamine uptake-deficient mutant. This and related observations demonstrate that AzhepSi and EtAzhepSi are preferentially taken up by a polyamine transport system. Both tetramines inhibit the growth of a variety of tumor cells at micromolar concentrations. AzhepSi turned out to be either equipotent or more potent, but in no case less potent than EtAzhepSi. When given alone at daily doses of 25 micromol/kg, the compounds did not prolong the survival time of L1210 leukemia mice. However, in combination with 2-(difluoromethyl)ornithine and neomycin, AzhepSi had a significant effect on the life span of the animals. The growth rate of 3LL Lewis lung carcinoma was reduced by both compounds at daily doses of 25 micromol/kg. The observations presented in this work suggest that the dimethylsilyl tetramines are antiproliferative agents in vitro and in vivo. Due to enhanced general toxicity, the introduction of N-ethyl substituents was of no advantage in the case of these polyamine analogues.

Animals↗
PubMed1996

Polyamine transport in mammalian cells. An update.

The uptake and release of the natural polyamines putrescine, spermidine and spermine by mammalian cells are integral parts of the systems that regulate the intracellular concentrations of these biogenic amines according to needs. Although a general feature of all tissues, polyamine uptake into intestinal mucosa cells is perhaps the most obvious polyamine transport pathway of physiological and pathophysiological importance. Mutant cell lines lacking the ability to take up polyamines from the environment are capable of releasing polyamines. This indicates that uptake and release are functions of two different transport systems. The isolation of a transporter gene from a mammalian cell line is still lacking. Overaccumulation of polyamines is controlled by release and by a feedback regulation system that involves de novo synthesis of antizyme, a well known protein that also regulates the activity of ornithine decarboxylase. Recent work has demonstrated that Ca(2+)-signalling pathways are also involved. Although there is consensus about the importance of polyamine uptake inhibitors in the treatment of neoplastic disorders, a practically useful uptake inhibitor is still missing. However, the attempts to target tumours, and to increase the selectivity of cytotoxic agents by combining them with the polyamine structure, are promising. New, less toxic and more selective anticancer drugs can be expected from this approach.

Animals↗
PubMed1996

Observations with an S-adenosylmethionine decarboxylase inhibitor in rats with prostatic adenocarcinoma.

CGP 48664A (2-(4-aminoiminomethyl)-2,3-dihydro-1H-inden-1-ylidene dihydrochloride, CAS 149400-88-4) is a new potent inhibitor of S-adenosylmethionine decarboxylase with antitumor properties. In view of the eminent clinical problems in the treatment of non hormone dependent prostatic cancer, the antiproliferative potency of this compound was tested in Dunning MAT-LyLu rat prostatic adenocarcinoma. The compound proved inefficient in preventing the growth of this tumor, even at a near toxic dose. A reason for the lacking effect is presumably the inadequate accumulation of the drug in the tumor cells due to the excessive growth rate of the MAT-LyLu xenografts. Tumor growth seems not to be accompanied by a proportionally rapid vascularization of the tumor mass. CGP 48664A was found to be a potent inhibitor of polyamine oxidase. This property of the drug may have contributed to the activation of the phagocytic capacity of peritoneal macrophages from tumor-bearing rats.

Adenocarcinoma↗
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↗
PubMed1995

Polyamine oxidase, properties and functions.

Polyamine oxidase (PAO) is a FAD-dependent enzyme with a molecular mass of about 62 kDa, present with high activity in most tissues of vertebrates. Structural requirements of a substrate for PAO are two positively charged amino groups, separated by a short carbon chain and an alkyl substituent on one or both nitrogen atoms. Spermine and the monoacetyl derivatives N1-acetylspermine and N1-acetylspermidine appear to be the natural substrates. Spermidine is only poorly oxidized by PAO. Using O2, the substrates are oxidatively cleaved by PAO to form equimolar amounts of an amine, an aldehyde and hydrogen peroxide. PAO is an integral part of the polyamine interconversion cycle, a major intracellular regulatory system, which contributes to the maintenance of polyamine homeostasis in non-proliferating cells, including brain cells. Selective inactivators were used as tools in the elucidation of the functions of PAO. Interestingly, even long-term inactivation of PAO did not provoke behavioral changes in experimental animals, despite considerable changes in polyamine metabolism. PAO inactivation, however, improves the growth-inhibitory effects of inhibitors of polyamine biosynthetic enzymes and the antitumoral effects of some structural analogs of the polyamines.

Age Factors↗
PubMed1995

Beneficial effects of L-arginine on intestinal epithelial restitution after ischemic damage in rats.

The polyamines are involved in repair processes after intestinal ischemia. Arginine and ornithine, both precursors of polyamines were therefore expected to exert beneficial effects on mucosal barrier dysfunction. Arginine may also generate NO and there is support for the view that NO may be beneficial after an ischemic insult. Male Wistar rats were given, by gavage, isonitrogenous solutions of L-arginine (0.5 g/kg) or L-ornithine (0.7 g/kg) 17 and 2 h before ischemia. Controls received an isonitrogenous solution of casein hydrolysate (1 g/kg). Transient intestinal ischemia was produced in anesthetized rats by occluding the superior mesenteric artery for 90 min. Intestinal morphology, hydrolase activities, polyamine and cGMP contents, and cell proliferation rates were determined 4 h after reperfusion. Administration of arginine or ornithine did not prevent ischemic damage but accelerated morphological repair, enhanced cell proliferation, and polyamine content was observed. Arginine was significantly more effective than ornithine. Formation of cGMP was enhanced after arginine administration. NG-nitroarginine methylester, an inhibitor of NO synthase, prevented the arginine effects on mucosal repair. We conclude that arginine-derived NO is an important mediator in the restitution of intestinal mucosa by minimizing cell injury during reperfusion.

Aminopeptidases↗
PubMed1994

Induction of low-affinity GABAA receptors by the GABA-agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) in cultured rat cerebellar granule cells is prevented by inhibition of polyamine biosynthesis.

GABAA agonist-induced formation of low-affinity GABAA receptors in cultured cerebellar granule cells was studied in the presence or absence of alpha-difluoromethylornithine (DFMO), a blocker of polyamine formation. High- and low-affinity GABAA receptors were monitored by Scatchard analysis of [3H]GABA binding to membranes from cells cultured for either 4 or 10 days in the presence or absence of the GABA agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). Cultures grown for 4 days were exposed to THIP and DFMO for an additional period of 6 hr (acute exposure), whereas cultures grown for 10 days were exposed to the same agents during the entire culture period (chronic exposure). Regardless of the culture period or drug exposure protocol, control cells expressed only a high-affinity (KD 7 nM) binding site for GABA, whereas the cultures treated with THIP for either 6 hr or 10 days exhibited an additional low-affinity binding site (KD approximately 500 nM). Chronic exposure to DFMO prevented the THIP induction of low-affinity GABAA receptors, whereas acute exposure to DFMO had no effect on the ability of THIP to induce low-affinity GABAA receptors. Measurements of the intracellular polyamine concentration demonstrated a slight decrease in the putrescine level in the granule cells exposed to DFMO or THIP + DFMO for 6 hr. In contrast, granule cells chronically (10 days) exposed to DFMO or THIP + DFMO were depleted of putrescine and spermidine. Hence, the ability of THIP to induce low-affinity GABAA receptors was prevented by the simultaneous depletion of the cellular content of putrescine and spermidine, whereas inhibition of ornithine decarboxylase and of putrescine formation was not sufficient to prevent THIP-induced receptor formation.

Animals↗
PubMed1994

Characterization of a COS cell line deficient in polyamine transport.

In the present study, we describe the isolation and characterization of a COS cell line deficient in polyamine uptake that may provide an important tool for the molecular cloning of polyamine transporter(s). The cells were selected by isolation for resistance against the cytotoxic agent, methylglyoxal bis(guanylhydrazone) (MGBG), which is entering the cells using the same transport system as the polyamines. The isolated cell line was capable of growing in the presence of 100 microM MGBG, which totally inhibited the growth of the wild-type cells. The transport of putrescine and spermidine was markedly decreased in the COS-MGBGr cells. The decrease in putrescine transport was mainly a result of a 14-fold decrease in Vmax, whereas the reduced spermidine uptake was due to a 3-4-fold decrease in Vmax as well as 12-fold increase in Km, indicating the existence of at least two separate transport systems. No major difference in polyamine content was seen between the parental and the COS-MGBGr cells when grown without MGBG. In the presence of MGBG, both cell lines exhibited an increase in putrescine content. Treatment with MGBG also resulted in a decrease in spermidine and spermine contents in the wild-type cells. In the COS-MGBGr cells, on the other hand, there were no statistically significant effects on the spermidine and spermine contents by MGBG treatment. In the wild-type cells, depletion of polyamines, e.g., by treatment with the ornithine decarboxylase inhibitor 2-difluoromethylornithine (DFMO), stimulated the uptake of polyamines (3-7-fold), whereas in the COS-MGBGr cells the effect of DFMO treatment on polyamine transport was only minor. In contrast to the growth-medium of the wild-type cells, large amounts of polyamines accumulated in the medium of the COS-MGBGr cells, presumably indicating that COS cells normally excrete polyamines and then salvage them using the polyamine transport system.

Animals↗
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↗