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Biomedical subjects

A Brossi

Publications and source records attributed to A Brossi.

At least 73 records · Page 4Linked to original sources
PubMed1986

Inhibition of acetylcholinesterase from electric eel by (-)-and (+)-physostigmine and related compounds.

Unnatural (+)-physostigmine (2) inhibited acetylcholinesterase (AChE) from electric eel considerably less than natural (-)-physostigmine (1), but 2 may because of its possible lower toxicity still be an interesting anticholinesterase agent. (-)-Eseroline (3), a major metabolite of (-)-physostigmine (1) and a potent narcotic analgetic, and its unnatural (+)-antipode (4), were both poor inhibitors of the enzyme. (-)-Dihydrosecophysostigmine (5), a ring-open analog of (-)-physostigmine was less, but (-)-N-methylphysostigmine (6) much more potent than the natural alkaloid. The availability of compounds related to (-)- and (+)-physostigmine by improved chemical synthesis suggests that further structural variation may well lead to other biologically interesting AChE inhibitors.

Acetylcholinesterase↗
PubMed1986

Studies on the mechanism of MPTP oxidation by human liver monoamine oxidase B.

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its deuterated analogues were oxidized to their corresponding dihydropyridinium species (MPDP+) by preparations of pure human liver MAO B:monoclonal antibody complex to investigate the mechanism of MPTP activation. Lineweaver-Burk plots of initial reaction rates revealed that the Km,app values for the various deuterated MPTP analogues were similar to those of MPTP. In contrast, Vmax,app values were substantially decreased by substitution of deuterium for hydrogen on the tetrahydropyridinium ring, especially at C-6. Deuterium substitution on the N-methyl group alone did not significantly reduce Vmax,app. These studies support the interpretation that oxidation of MPTP at the C-6 position on the tetrahydropyridine ring is a major rate-determining step in its biotransformation by MAO B.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

Biochemical changes caused by the infusion into the substantia nigra of the rat of MPTP and related compounds which antagonise dihydropteridine reductase.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenylpyridinium bromide (MPP+), 1-methyl-4-(3', 4'-dihydroxyphenyl)pyridinium bromide, 4-(3',4'-dihydroxyphenyl)pyridine, 4-phenyl-1,2,3,6-tetrahydropyridine and 4-(3',4'-dimethoxyphenyl)1,2,3,6-tetrahydropyridine were infused bilaterally into the substantia nigra of the rat (10 micrograms/24 hr for 4 days). The ability to inhibit spontaneous locomotor activity and to reduce levels of neurotransmitters and metabolites in the nigrostriatal system (striatum, substantia nigra) was compared with activity to inhibit dihydropteridine reductase (DHPR) in vitro. The compound MPP+ was most effective to reduce motor responding and to decrease levels of dopamine, DOPAC and HVA (50-56%) in the striatum in addition to reducing levels of dopamine, DOPAC, noradrenaline, serotonin and 5-HIAA (42-86%) in the substantia nigra, yet MPP+ has been shown to have very weak ability to inhibit DHPR. In contrast, 4-(3',4'-dihydroxyphenyl)pyridine and 1-methyl-4-(3',4'-dihydroxyphenyl)pyridinium bromide were in the order of 10(4) and 2 X 10(5) times, respectively, more potent than MPP+ to inhibit DHPR in vitro, but these compounds failed to modify dopamine neuronal function when assessed in vivo. Therefore, there would not appear to be any correlation between the ability to modify dopamine neuronal function, as assessed behaviourally or biochemically, and ability to inhibit DHPR in synaptosomes from the striatum of the rat in vitro.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

Comparison of (-)-eseroline with (+)-eseroline and dihydroseco analogues in antinociceptive assays: confirmation of rubreserine structure by X-ray analysis.

The enantiomers of eseroline bind to opiate receptors of rat brain membranes with equal affinities and show opiate agonist properties as inhibitors of adenylate cyclase in vitro. However, only (-)-eseroline shows potent narcotic agonist activity in vivo, similar to that of morphine. Neither (-)-noreseroline, (+)-eseroline, nor the open dihydroseco analogue (-)-8 shows analgetic effects in vivo. The structure of rubreserine being a resonance hybrid of an o-quinone with its zwitterionic mesomer is confirmed by solid-state X-ray diffraction analysis.

Adenylyl Cyclase Inhibitors↗
PubMed1986

Presence and formation of codeine and morphine in the rat.

Endogenous codeine and morphine were identified in rat brain by immunological determination following HPLC. To demonstrate occurrence of a biosynthetic pathway to morphine in mammals similar to that used by the poppy plant, (+)-salutaridine, (-)-thebaine, and (-)-codeine were administered to rats intravenously. These compounds, which are intermediates in the synthesis of morphine in Papaver somniferum, caused a marked increase in the codeine and morphine levels in rat tissues. This provides evidence for a biosynthetic pathway to morphine in mammalians.

Animals↗
PubMed1986

B ring regulation of colchicine binding kinetics and fluorescence.

Several properties of the colchicine-tubulin interaction such as association rate, reversibility, and the promotion of drug fluorescence have been related to the B ring of colchicine. The B ring itself retards the binding rate, and substitution at C-7 leads to further binding rate decreases that appear to be related to both substituent bulk and the presence of a N-acyl group. Thus, the decreasing order of binding rates is 2-methoxy-5-(2',3',4'-trimethoxyphenyl)tropone greater than deacetamidocolchicine greater than deacetylcolchicine greater than or equal to colcemid greater than colchicine greater than N-benzoyldeacetylcolchicine, etc. The apparent irreversibility of the binding seems more closely related to the presence of an N-acyl group rather than the bulk of the substituent at C-7. Substitution at C-7 also affects the tropolone fluorophore. Thus, amines (deacetylcholchicine, colcemid, or N-methylcolcemid) fluoresce poorly in the presence of tubulin, whereas substitution of the amino group with an acyl group enhances fluorescence. The presence of an N-acyl group at C-7 is essential for enhanced fluorescence. We conclude that, in addition to A- and the C-ring portion of the molecule, the B ring of colchicine is a third determinant recognized by the binding site on tubulin.

Animals↗
PubMed1985

Serotonergic conversion of MPTP and dopaminergic accumulation of MPP+.

[3H]MPP+ had lower Km and higher Vmax values for its accumulation in rat brain synaptosomes than did [3H]MPTP. The kinetic parameters favored the uptake of [3H]MPP+ in the striatum to that in hypothalamus, whereas they were equally favorable for the uptake of [3H]MPTP in both regions. Hypothalamic uptake of [3H]MPTP and [3H]MPP+ was inhibited by desipramine, imipramine, norepinephrine, and serotonin. Striatal uptake of [3H]MPP+ and [3H]MPTP was blocked by nomifensine and dopamine. These results support the concept that MPTP accumulates in serotonergic neurons where it is oxidized by monoamine oxidase B to MPP+, which is released and then is selectively accumulated in dopaminergic neurons via the dopamine uptake system.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1985

Metabolism of the neurotoxin in MPTP by human liver monoamine oxidase B.

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was oxidized to dihydropyridine MPDP+ and pyridine MPP+ by preparations of monoamine oxidase B (MAO B), including pure human liver MAO B:monoclonal antibody complex, Km,app values for MPTP and benzylamine, a preferred MAO B substrate, were 316 and 64 microM, respectively. 4-Phenyl-1,2,3,6-tetrahydropyridine (PTP), the nor derivative of MPTP, was also a substrate (Km,app = 221 microM). MPDP+, MPTP, and MPP+, but not PTP, were found to be irreversible inhibitors of MAO B. Our studies support the hypothesis that MPTP is oxidized in primate brain by MAO B to MPDP+, which is then converted to MPP+, a major metabolite found in the substantia nigra.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1985

Further insight into the mode of action of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

Chemical reactions of MPDP+, a recognized intermediate in the metabolic conversion of the neurotoxin MPTP by monoamine oxidase B into its major metabolite MPP+, were studied. Addition of cyanide to MPDP+ bromide in aqueous solutions afforded cyano-compound 5 which isomerized in the presence of silica gel into compound 6. Both 5 and 6 when heated yielded a third isomer 7. MPDP+ bromide disproportionated into MPTP and MPP+ in aqueous solution near neutral or slightly alkaline pH, a reaction which also occurred when MPDP+ bromide was treated with an amine in dichloromethane solution. Disproportionation of MPDP+ at physiological pH may be of biochemical significance, since formation of MPP+ from MPDP+ can occur non-enzymatically. MPTP, MPDP+, and MPP+ inhibited dopamine uptake in rat synaptosomal preparations with I50 values of 30, 37, and 3.4 microM, respectively. The competition of these compounds with dopamine for uptake sites in the membrane may contribute in part to the reduced levels of dopamine observed in animals treated with MPTP.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1985

Synthesis and biological effects of novel thiocolchicines. 3. Evaluation of N-acyldeacetylthiocolchicines, N-(alkoxycarbonyl) deacetylthiocolchicines, and O-ethyldemethylthiocolchicines. New synthesis of thiodemecolcine and antileukemic effects of 2-demethyl- and 3-demethylthiocolchicine.

Novel and known analogues of thiocolchicine were evaluated in vitro in a tubulin binding assay and in vivo in mice for acute toxicity and in the P388 lymphocytic leukemia assay. This evaluation included N-acyldeacetylthiocolchicines, N-(alkoxycarbonyl)deacetylthiocolchicines, thiodemecolcine and its methyl carbamate, and O-ethyl ethers of demethylthiocolchicines. Selective ether cleavage of thiodemecolcine with concentrated sulfuric acid at 50 degree C afforded the 2-demethyl congener, characterized as its N,O-diacetyl derivative. Several of the compounds showed high potency in the tubulin binding assay, matching the potency of colchicine. Several N-(alkoxycarbonyl)deacetylcolchicines (carbamates) exhibited strong binding affinity to tubulin but had only weak activities against the P388 tumor system, suggesting that other factors besides tubulin binding may be important for the biological effects. The compounds potent in the tubulin binding assay and in the P388 leukemia assay in mice were generally also toxic to mice in the acute toxicity test, showing thus a similar behavior of thiocolchicines to that observed earlier with colchicines. A considerable amount of data collected for 2-demethyl- and 3-demethylthiocolchicine suggests that the latter represents a broad-spectrum antitumor agent of considerable promise and possibly a less toxic substitute for colchicine.

Animals↗
PubMed1985

Synthesis and dihydropteridine reductase inhibitory effects of potential metabolites of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a nigrostriatal neurotoxin which can cause irreversible parkinsonism in humans and primates by selective destruction of neurons in the substantia nigra. It is possible that MPTP could be metabolized by hydroxylation of the phenyl ring and/or aromatization of its nitrogen-containing ring. Hydroxylated derivatives of 4-phenyl-1,2,3,6-tetrahydropyridine, 4-phenylpiperidine, and 4-phenylpyridine were synthesized and tested in vitro as inhibitors of dihydropteridine reductase (DHPR) from human liver and rat striatal synaptosomes. It was found that all hydroxy derivatives were about 100-10 000 times more inhibitory than MPTP to DHPR. The inhibitory potency of the hydroxylated derivatives increased with the number of hydroxyl substitutions present on the phenyl ring (catechol greater than phenol) and with oxidation of the nitrogen-containing ring (pyridine greater than tetrahydropyridine greater than piperidine).

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1984

Inhibition of dihydropteridine reductase by novel 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine analogs.

Hydroxylated derivatives of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a nigrostriatal neurotoxin in humans and primates, noncompetitively inhibited dihydropteridine reductase from human liver and rat striatal synaptosomes in vitro at micromolar concentrations. In contrast, MPTP and its chloro- and norderivatives did not inhibit this enzyme at lower than millimolar concentrations. Dihydropteridine reductase converts dihydrobiopterin to tetrahydrobiopterin, the required cofactor for the hydroxylation of aromatic amino acids during the synthesis of dopamine and serotonin.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1984

Synthesis and binding to tubulin of colchicine spin probes.

Spin probes of deacetylcholchicine (1), 4-(hydroxymethyl)colchicine (2), and colchifoline (3) have been synthesized to study the binding site for colchicine on tubulin. Acylation of 1-3 with (+/-)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy-3-carboxylic acid (4) afforded diastereomeric mixtures of the esters 5-8 and the amides 9 and 10. Pure diastereomers of 3 were synthesized with 4a and 4b, which inhibited the binding of colchicine by 60%. In the presence of calf brain microtubular protein, the colchifoline spin labels underwent reduction of the nitroxide group, which precluded their use to study the topography of the colchicine binding site.

Animals↗
PubMed1984

A study of the novel synthetic analog (+/-)-depentylperhydrohistrionicotoxin on the nicotinic receptor-ion channel complex.

(+/-)-Depentylperhydrohistrionicotoxin [(+/-)-depentyl-H12-HTX] is a synthetic analog of perhydrohistrionicotoxin (H12-HTX) that lacks the 5-carbon side chain. Recent studies with N-benzylazaspiro analogs of histrionicotoxin (HTX) in which both side chains are removed revealed that this alteration restricted the action of the compounds on the acetylcholine receptor-ionic channel complex (AChR) to an open channel blockade. Thus, an important question was raised as to the role of the side chains in affecting the interaction of these inhibitors with the AChR. In addition, the effect of (+/-)-depentyl-H12-HTX on membrane excitability was investigated. (+/-)-Depentyl-H12-HTX blocked the indirectly elicited twitch without affecting the directly elicited twitch. It decreased the amplitude and rate of rise and prolonged the falling phase of the action potential and blocked delayed rectification suggestive of blockade of sodium and potassium conductances. However, its effects on sodium and potassium conductances were less marked than those of HTX. It decreased the peak amplitude of the end-plate currents (EPCs) and accelerated the decay time constant of EPCs (tau EPC) in a concentration-dependent manner. The analog also induced voltage- and time-dependent nonlinearity in the current-voltage relationship of EPCs. Despite marked shortening of tau EPC, the decay phase of the EPC remained a single exponential function of time. Single channel conductance was unaffected by the analog, but the single channel lifetime was shortened. The voltage- and time-dependent effects of the analog that occurred without prior activation of AChR suggest reaction with the ionic channel in its closed conformation.

Acetylcholine↗
PubMed1984

Interaction of analogs of histrionicotoxin with the acetylcholine receptor ionic channel complex and membrane excitability.

The effects of the four N-benzylazaspiro analogs of histrionicotoxin, which are without the two side-chains typical of histrionicotoxin, were studied on the ionic channels of electrically excitable membrane and the nicotinic acetylcholine receptors in frog sartorius muscles. Each analog reversibly blocked the indirectly elicited twitch and potentiated the directly elicited twitch in a concentration-dependent manner. The analogs decreased the amplitude and rate of rise and prolonged the falling phase of the directly elicited action potential and blocked delayed rectification suggesting blockade of sodium and potassium conductances. All of the analogs caused a concentration- and voltage-dependent depression of the peak end-plate current amplitude and induced nonlinearity but no hysteresis or time dependency in the current-voltage relationship. The marked shortening of the time constant of end-plate current decay produced by the analogs was concentration-dependent. The relationship between the time constant of end-plate current decay and membrane potential remained a single exponential function of time despite the marked shortening of the decay phase and loss of voltage dependence. The effect of the analogs on miniature end-plate current was identical to that on end-plate current. Single channel conductance was unaffected by the analogs, but the single channel lifetime was shortened. The marked shortening of the time constant of the end-plate current decay and single channel lifetime plus linear relationship between reciprocal of the time constant of decay and analog concentrations strongly suggest that the analogs interact with the ionic channels of the nicotinic acetylcholine receptor in their open conformation.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1983

The ionic channel of the nicotinic acetylcholine receptor is unable to differentiate between the optical antipodes of perhydrohistrionicotoxin.

The enantiomers of perhydrohistrionicotoxin were studied in their effects on endplate currents recorded at the junctional region of sartorius muscles of Rana pipiens. The two optical antipodes progressively decreased the peak amplitude of the endplate currents and were indistinguishable from each other at all times. The enantiomers shortened equally the time constants for endplate current decay, but did not alter their voltage sensitivities. Although perhydrohistrionicotoxin contains 4 chiral centers, complete steric inversion does not alter its effects on the acetylcholine receptor-ion channel complex. By contrast the recognition site of the AcChR is extremely sensitive to any change in the chirality of agonists.

Amphibian Venoms↗
PubMed1983

Biological effects of modified colchicines. 2. Evaluation of catecholic colchicines, colchifolines, colchicide, and novel N-acyl- and N-aroyldeacetylcolchicines.

A series of natural and synthetic colchicine derivatives was examined for their potency in the lymphocytic leukemia P388 screen in mice, for their toxicity in mice, and for their binding to microtubule protein. The natural alkaloids cornigerine and colchifoline and several N,O-substituted analogues of colchifoline were found to be as potent and as toxic as colchicine in the P388 screen with good affinity for tubulin. The 1,2-(methylenedioxy)-substituted isomer of cornigerine was considerably less potent in vivo than could have been anticipated from the in vitro tubulin binding data. Several N-acyl and N-aroyl derivatives prepared from deacetylcolchicine showed high potency in the in vitro and in vivo screens. Colchicide was found to be highly potent in vivo, and N-carbethoxydeacetylcolchicine, a synthetic analogue of colchicine with a N-carbethoxy instead of an N-acetyl function, showed interesting biological properties.

Animals↗