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Biomedical subjects

E Hamel

Publications and source records attributed to E Hamel.

At least 253 records · Page 14Linked to original sources
PubMed1981

Effects of inhibitors of tubulin polymerization on GTP hydrolysis.

The effects of a number of antimitotic drugs on the GTPase activity of tubulin were examined. The previously reported stimulation with colchicine and inhibition with podophyllotoxin and vinblastine wee confirmed. Maytansine, which competes with vinblastine in binding to tubulin, was comparable to the latter in inhibiting GTP hydrolysis. Nocodazole, which competes with colchicine in binding to tubulin, was significantly superior to colchicine in enhancing GTP hydrolysis. This superiority arose from the more rapid bindng of nocodazole to tubulin, as the two drugs had comparable activity when drug and tubulin were preincubated prior to the addition of GTP. Both colchicine and podophyllotoxin contain a trimethoxybenzene ring, while the closest structural analogy of nocodazole to colchicine includes the trimethoxybenzene ring. To explore this apparent paradox, we examined a number of simpler colchicine analogs for their effects on tubulin-dependent GTP hydrolysis. While tropolone was without effect, 3,4,5-trimethoxybenzaldehyde and 2,3,4-trimethoxybenzaldehyde stimulated the reaction. We therefore conclude that the trimethoxybenzene ring of colchicine is primarily responsible for the drug's stimulation of the GTPase activity of tubulin and that the inhibitory effect of podophyllotoxin must derive from the latter's tetrahydronaphthol moiety.

Animals↗
PubMed1981

Stabilization of the colchicine-binding activity of tubulin by organic acids.

A number of carboxylic acids and organic phosphates were found to be highly effective in stabilizing the colchicine-binding activity of calf brain tubulin. The most active were glutamate, glutarate, delta-aminovalerate, glucose 1-phosphate, glucose 6-phosphate, fructose 1,6-(bis)phosphate, creatine phosphate and 6-phosphogluconate Maximum effects occurred at high concentrations. Combinations of agents were also examined, and the most effective mixture for stabilizing tubulin found thus far was the combination of 1.0 M glutamate, 100 mM glucose 1-phosphate, 1 mM GTP and 0.5 mg/ml of albumin. No loss of activity occurred over 48 h at 37 degrees C with tubulin was present at a concentration of 100 microgram/ml.

Animals↗
PubMed1981

Interaction of tubulin with ribose-modified analogs of GTP and GDP: evidence for two mutually exclusive exchangeable nucleotide binding sites.

Interactions of tubulin with a number of guanine nucleotides modified at the 2' and 3' ribose hydroxyls were examined. Deoxy analogs of GTP were equal or superior to GTP in supporting tubulin polymerization, but analogs bearing either methyl or phosphate groups on the hydroxyls had significantly reduced ability to support polymerization. These substituted GTP analogs were hydrolyzed at the 5'-gamma-phosphate position, although less rapidly than GTP, at rates exceeding those of polymerization. GTP hydrolysis, however, was closely coupled to polymerization. Moreover, the partially active GTP analogs were not effective inhibitors of GTP-dependent polymerization. These data indicate that the substituted GTP analogs have reduced affinity for tubulin at the exchangeable site because of steric factors. No deoxy or substituted GDP analog was as effective as GDP itself in inhibiting GTP-supported tubulin polymerization. Furthermore, there was no apparent relationship between the ability of nucleoside 5'-triphosphates to support polymerization and that of nucleoside 5'-diphosphates to inhibit the reaction. These findings suggest that GTP and GDP may actually bind to different, mutually exclusive sites rather than to a single exchangeable site.

Animals↗
PubMed1981

Induction of polymerization of purified tubulin by sulfonate buffers. Marked differences between 4-morpholineethanesulfonate (Mes) and 1,4-piperazineethanesulfonate (Pipes).

Interactions of both purified tubulin and microtubule protein (tubulin plus associated proteins) with two commonly used sulfonate buffers were examined. 1,4-Piperazineethanesulfonate (Pipes) and 4-morpholineethanesulfonate (Mes) at high concentrations induce the polymerization of purified tubulin in reactions requiring only buffer, tubulin and GTP. While both reactions were temperature-dependent, cold-reversible and inhibited by GDP, colchicine or Ca2+, there were significant differences between them. Substantially lower tubulin and buffer concentrations were required for Pipes-induced polymerization; and turbidity was much more intense in the Pipes-induced than in the Mes-induced reaction at the same protein concentration. Electron microscopy demonstrated that for the most part typical smooth-walled microtubules were formed in Mes, while aberrant forms were the predominant structures formed in Pipes. When the polymerization of microtubule protein was examined as a function of buffer concentration, biphasic patterns were observed with both Pipes and Mes: polymerization occurred at both low and high, but not intermediate, buffer concentrations. The turbidity observed at high concentrations of Pipes greatly exceeded that at low concentrations. With Mes, equivalent turbidity developed at both high and low buffer concentrations. Although associated proteins copolymerized with tubulin at low buffer concentrations, they were excluded from the polymerized material at high buffer concentrations. Pipes and Mes were compared to sodium phosphate, Tris/HCl and imidazole/HCl buffers at 0.1 M in several polymerization systems using both purified tubulin and microtubule protein. The sulfonate buffers were invariably associated with more vigorous reactions than the other buffers.

Alkanesulfonates↗
PubMed1981

Glutamic acid decarboxylase and gamma-aminobutyric acid in Huntington's disease fibroblasts and other cultured cells, determined by a [3H]muscimol radioreceptor assay.

A sensitive and reproducible [3H]muscimol radioreceptor assay was developed for measuring low levels of both glutamic acid decarboxylase activity and gamma-aminobutyric acid. By using this technique, endogenous gamma-aminobutyric acid and glutamic acid decarboxylase activity were detected in two rat neuroblastomas, B35 and B50, a human medulloblastoma cell line, TE671, and cultured human skin fibroblasts. Glutamic acid decarboxylase activities and gamma-aminobutyric acid levels were compared for human skin fibroblasts obtained from patients with Huntington's disease and their controls in a well-controlled, blind study. However, no significant difference was found to either measure between Huntington and control cells. Glutamic acid decarboxylase activity was relatively low in all cell types examined except for the TE671 cells, which had more than four times the activity found in the other cells. This human medulloblastoma cell line appears to be a good model for studying gamma-aminobutyric acid metabolism and the control of glutamic acid decarboxylase expression.

Carboxy-Lyases↗
PubMed1981

Binding of maytansine to tubulin: competition with other mitotic inhibitors.

The effect of maytansine on the binding of [3H]vinblastine and [3H]colchicine to tubulin was examined by Sephadex gel filtration column chromatography. When varying concentrations of maytansine were employed, competition between vinblastine and maytansine was observed at a vinblastine to maytansine ratio of 1:10 and 1:100, while a colchicine to maytansine ratio of 1:100 did not affect the binding of colchicine to tubulin. These results confirm earlier findings with a DEAE-cellulose disc paper assay and a tubulin polymerization assay that maytansine shares a common binding site with vinblastine and support the view that tubulin has at least two drug binding sites.

Animals↗
PubMed1980

Intracranial intradural epidermoids and dermoids. Surgical results of 38 cases.

This report covers 38 Cases of intradural dermoids (4 cases) and epidermoids (34 cases). In most cases the clinical course extended over several years. At the time of admission to the clinic only 9 patients had purely local symptoms; symptoms from adjacent areas were present in 15 cases and elevated intracranial pressure in 13. Of the 35 operated patients, 16 were able to work again, and 7 died after the operation. Best results are achieved in cases involving young patients, in cases where the tumor is situated in the cerebral hemisphere, and in cases where the tumor can be totally removed. In recent years advances in diagnostic, surgical and anaesthetic techniques have lowered the lethality rate. Computed tomography is especially useful for an early diagnosis.

Adolescent↗
PubMed1980

Effect of asparagine, glutamine and insulin on cerebral amino acid neurotransmitters.

Treatment of rats with asparagine or glutamine caused substantial increases in glutamine concentrations in cerebellum and medulla oblongata. Insulin treatment caused a diminution of glutamate and GABA in these regions of brain. Since it is now well-established that glutamine is a very efficient precursor of the neurotransmitter pool of glutamate in mammalian brain, treatment with asparagine or glutamine could be of therapeutic (replacement) value in the treatment of neurological disorders such as Friedreich's ataxia, in which cerebral glutamate concentrations have been found to be diminished.

Animals↗
PubMed1979

Measurement of ataxia and related neurological signs in the laboratory rat.

The purpose of the present study was to design a standard battery of tests capable of quantitatively characterizing ataxia and concomitant neurological signs in the rat. In addition to a systematic analysis of the walking gait of animals, tests for activity, catalepsy, rigidity, and various reflexive responses were included in the battery. The standardization and validation of the test system was performed by determining and comparing profiles of neurobehavioral effects produced by 3-acetyl pyridine, acrylamide, pyrithiamine, and thiamine deficiency, four experimental treatments reported to induce ataxia in animals. Results indicate that profiles of neurobehavioral disturbances accompanying ataxia in animals varied distinctively with each experimental treatment.

Acrylamides↗
PubMed1979

Amino acid changes in thiamine-deficient encephalopathy: some implications for the pathogenesis of Friedreich's ataxia.

Thiamine-deficient encephalopathy in the rat is characterized by ataxic gait, loss of righting reflex and curvature of the spine. Neurochemical changes include a diminished activity of cerebral pyruvate decarboxylase leading to abnormal pyruvate oxidation. The present study shows that this defective pyruvate oxidation produces a significant depletion of three important amino acid neurotransmitters, namely gamma aminobutyric acid (GABA), glutamic acid, and aspartic acid. Such changes could lead to severe neuronal dysfunction and the observed neurological symptoms of thiamine deficiency. Some implications for the pathogenesis of Friedreich's ataxia are discussed.

Amino Acids↗
PubMed1978

Effects of cocaine on rat pancreatic enzyme secretion and protein synthesis.

The effects of cocaine on amylase secretion and total protein synthesis was studied by use of vitro rat pancreatic tissue. In vitro, cocaine (2 or 10 mM) did not modify basal release of amylase; at a concentration of 2 mM, it reduced the secretory response to pancreozymin by 32% and that to urecholine by 68%. Incorporation of amino acids into total proteins was decreased by 15% by cocaine 2 mM and by 49.5% at 10 mM. Administered in vivo at a dose of 15 mg/kg intraperitoneally, cocaine was associated with decreased in protein synthesis 30, 90, and 180 min after its injection. These results indicate that cocaine can affect basic functions of the exocrine pancreas and reduce its response to secretagogues.

Amylases↗
PubMed1978

Familial hyperbilirubinemia in Friedreich's ataxia.

The combined metabolic stresses of fasting and the intravenous injection of 50 mg nicotinic acid in Friedreich's ataxia resulted in the delineation of two sub-groups of responses. High bilirubin ataxics maintained abnormally elevated levels of bilirubin, while normal bilirubin ataxics behaved like the normal control group. It is postulated that this finding infers the possible linkage of the gene for Friedreich's ataxia and that for Gilbert's disease.

Bilirubin↗
PubMed1978

Cerebellar ataxia produced by 3-acetyl pyridine in rat.

A single intraperitoneal injection of 3-acetyl pyridine produces, within 24 hours of administration, signs of cerebellar ataxia and damage to the medulla oblongata and to the climbing fibers of the cerebellum. These changes are accompanied by changes in the concentration of certain amino acids in the appropriate areas. Glutamic acid is decreased in cerebellum, medulla, cortex, striatum, hippocampus, retina and olfactory bulbs, while taurine is specifically decreased in the cerebellum and medulla oblongata and aspartic acid in the retina. The concentrations of GABA and glycine are not modified in any of the areas studied. Glutamine is generally increased in concentration in areas of cell damage.

Amino Acids↗
PubMed1978

Effect of alloxan diabetes on cerebellar amino acids.

Rats rendered diabetic by alloxan monohydrate were studied to investigate the effect of increased blood glucose upon the concentration of various putative neurotransmitter amino acids in the cerebellum. No modification was found in the concentrations of glutamate, gamma aminobutyric acid (GABA), glutamine, glycine or taurine, but there was a significant decrease in the cerebellar concentration of aspartate in the diabetic animals. This raises the question of the specificity of the aspartic acid defect found in some form of ataxia.

Amino Acids↗
PubMed1976

Derivatives of guanosine triphosphate with ribose 2'-hydroxyl substituents. Interactions with the protein synthetic enzymes of Escherichia coli.

This report describes the preparation of four methylated and phosphorylated derivatives of GTP, 2'-O-methylguanosine 5'-triphosphate (PPP-Me2' Guo), and guanosine 2'-monophosphate 5'-triphosphate (PPP-Guo-2'P), 3'-O-methylguanosine 5'-triphosphate (PPP-Me3'Guo), and guanosine 3'-monophosphate 5'-triphosphate (PPP-Guo-3'P). These compounds were compared to GTP in their ability to support reactions catalyzed by Escherichia coli initiation factor 2(IF-2), elongation factor Tu (EF-Tu), and elongation factor G )EF-G). As with previously studied GTP analogues, the nucleotide specificities of IF-2-dependent N-formylmethionylpuromycin formation and EF-Tu-dependent Ac-Phe2-tRNA formation were similar. There was little difference between the reactions supported by GTP, PPP-Me2' Guo, PPP-Me3' Guo, and PPP-Guo-3'P, but PPP-Guo-2'P was a poor substrate with both enzymes. A spectrum of activity was observed in EF-G-dependent formation of N-acetylphenylalanylphenylalanylpuromycin. While PPP-Me2' Guo was almost as effective as GTP in supporting translocation, PPP-Guo-2'P was a very poor substrate, having even less activity than guanosine 3'-diphosphate 5'-triphosphate. Intermediate activities were observed with PPP-Me3' Guo and PPP-Guo-3'P, the former nucleotide being more active than the latter.

Escherichia coli↗