Subtype-selective inhibition of [methyl-3H]-N-methylscopolamine binding to muscarinic receptors by alpha-truxillic acid esters.

Seven esters of alpha-truxillic acid have been synthesized: bis-3-piperidylpropyl ester and its quaternary bis-N-ethyl derivative, bis-N-diethylaminopropyl ester and its quaternary bis-N-methyl derivative, and bis-4-piperidylbutyl ester and its quaternary bis-N-methyl and bis-N-ethyl derivatives. All esters inhibited the specific binding of muscarinic receptor antagonist [methyl-3H]-N-methylscopolamine ([3H]-NMS) to muscarinic receptors in membranes of CHO cell lines stably expressing the human gene for the M1, M2, M3 or M4 subtype of muscarinic receptors. All esters displayed the highest potency at the M2 and the lowest potency at the M3 receptor subtype. In experiments performed on the M2 muscarinic receptor subtype, the affinity between the receptors and the esters was greatly increased when the concentration of ions was diminished. The highest affinities were found for the tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters (equilibrium dissociation constants of 52 and 179 pM, respectively, in the low ionic strength medium). All investigated esters slowed down the dissociation of [3H]-NMS from the M2 muscarinic receptor subtype. [3H]-NMS dissociation from the M1, M3 and M4 muscarinic receptor subtypes was investigated in experiments with the bis-4-piperidylbutyl aminoester and also found to be decelerated. It is concluded that the esters of alpha-truxillic acid act as M2-selective allosteric modulators of muscarinic receptors and that, by their potency, the tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters surpass the other known allosteric modulators of these receptors.

Tricyclic antidepressant binding to lymphocyte membranes and changes during depression.

The binding of [3H]imipramine, its 2- and 4-nitroderivatives and [3H]desmethylimipramine to lymphocyte membranes was determined. IC50 values for drugs and neurotransmitters to inhibit [3H]imipramine binding to lymphocyte membranes were comparable with those for brain and thrombocyte membranes. The number of [3H]imipramine and [3H]desmethylimipramine binding sites increased in depressive patients, whereas the dissociation constants remained unchanged.

In vitro glycosidation potential towards olomoucine-type cyclin-dependent kinase inhibitors in rodent and primate microsomes.

Interspecies differences in glycosidation potential in mammalian tissues represent a factor contributing to ambiguity when endobiotic and/or xenobiotic metabolic pathways are extrapolated from animals to man. Using the TLC/autoradiographic technique, we conducted an in vitro investigation involving mouse, rat, monkey, as well as human liver and kidney microsomes to evaluate their glycoconjugation potential towards (3)H-labeled, purine-derived selective inhibitors of cyclin-dependent kinases such as olomoucine, bohemine, roscovitine, 6-(2-hydroxybenzyl)amino-2-(1-hydroxymethyl-2-methylpropyl)amino-9-isopropylpurine (compound A-4), and 6-(3-hydroxybenzyl)amino-2-[(1(R/S)-hydroxymethyl)propyl]amino-9-isopropylpurine (compound A-5) as aglycones. Principally, this study confirmed the aliphatic hydroxyl group of olomoucine-type inhibitors as a relatively suitable target for glucuronide, glucoside, xyloside, galactoside, and/or N-acetylaminoglucoside conjugation. Of the tissues examined, only the mouse microsomes were able to perform glucosidation and galactosidation reactions with the aglycones. On the other hand, monkey microsomes were superior to the mouse microsomes in a variety of glucuronide conjugates produced with compounds A-4 and A-5.

Trichloroacetic acid in Norway spruce/soil-system. I. Biodegradation in soil.

Trichloroacetic acid (TCA) as a phytotoxic substance affects health status of coniferous trees. It is known as a secondary air pollutant (formed by photooxidation of tetrachloroethene and 1,1,1-trichloroethane) and as a product of chlorination of humic substances in soil. Its break-down in soil, however, influences considerably the TCA level, i.e. the extent of TCA uptake by spruce roots. In connection with our investigations of TCA effects on Norway spruce, microbial processes in soil were studied using 14C-labeling. It was shown that TCA degradation in soil is a fast process depending on TCA concentration, soil properties, humidity and temperature. As a result, the TCA level in soil is determined by a steady state between uptake from the atmosphere, formation in soil, leaching and degradation. The process of TCA degradation in soil thus participates significantly in the chlorine cycle in forest ecosystems.

Uptake, translocation and fate of trichloroacetic acid in a Norway spruce/soil system.

Trichloroacetic acid (TCA) is a secondary atmospheric pollutant formed by photooxidation of chlorinated solvents in the troposphere--it has, however, recently been ranked among natural organohalogens. Its herbicidal properties might be one of the factors adversely affecting forest health. TCA accumulates rapidly in conifer needles and influences the detoxification capacity in the trees. The aim of the investigations--a survey of which is briefly given here--was to elucidate the uptake, distribution and fate of TCA in Norway spruce. For this purpose young nursery-grown plants of Norway spruce (Picea abies (L.) Karst.) were exposed to [1,2-14C]TCA and the fate of the compound was followed in needles, wood, roots, soil and air with appropriate radio-indicator methods. As shown by radioactivity monitoring, the uptake of TCA from soil by roots proceeded most rapidly into current needles at the beginning of the TCA treatment and was redistributed at later dates so that TCA content in older needles increased. The only product of TCA metabolism/biodegradation found in the plant/soil-system was CO(2) (and corresponding assimilates). TCA biodegradation in soil depends on TCA concentration, soil humidity and other factors.

Trichloroacetic acid in Norway spruce/soil-system. II. Distribution and degradation in the plant.

Independently from its origin, trichloroacetic acid (TCA) as a phytotoxic substance affects coniferous trees. Its uptake, distribution and degradation were thus investigated in the Norway spruce/soil-system using 14C labeling. TCA is distributed in the tree mainly by the transpiration stream. As in soil, TCA seems to be degraded microbially, presumably by phyllosphere microorganisms in spruce needles. Indication of TCA biodegradation in trees is shown using both antibiotics and axenic plants.

Methylated and demethylated tricyclic antidepressants and their binding to cell membranes.

We studied the binding of methylated and demethylated tricyclic antidepressants (TCA) to synaptic plasma brain membranes (SPM) and to lymphocyte, platelet and erythrocyte membranes. In the synaptic plasma membranes, more demethylated than methylated dibenzazepine derivatives were bound and the binding affinity was decreased. By contrast, in lymphocyte and platelet membranes more methylated derivatives were bound. Phosphatidylserine (PS) enhanced significantly the binding of methylated TCA in SPM without changing the dissociation constant (Kd). Lysophosphatidylserine did not affect the binding. PS also caused an increase of 3H-imipramine binding to lymphocyte membranes but the binding to platelet membranes was not affected. PS also enhanced 3H-5-HT uptake into platelets and 3H-noradrenaline uptake into lymphocytes.

Binding of imipramine to phospholipid bilayers using radioligand binding assay.

Binding of the tricyclic antidepressant imipramine (IMI) to neutral and negatively charged lipid membranes was investigated using a radioligand binding assay combined with centrifugation or filtration. Lipid bilayers were composed of brain phosphatidylcholine (PC) and phosphatidylserine (PS). IMI binding isotherms were measured up to IMI concentration of 0.5 mmol/l. Due to electrostatic attraction, binding between the positively charged IMI and the negatively charged surfaces of PS membranes was augmented compared to binding to neutral PC membranes. After correction for electrostatic effects by means of the Gouy-Chapman theory, the binding isotherms were described both by surface partition coefficients and by binding parameters (association constants and binding capacities). It was confirmed that binding of IMI to model membranes is strongly affected by negatively charged phospholipids and that the binding is heterogeneous; in fact, weak surface adsorption and incorporation of the drug into the hydrophobic core of lipid bilayer can be seen and characterized. These results support the hypothesis suggesting that the lipid part of biological membranes plays a role in the mechanism of antidepressant action.

Imipramine distribution among red blood cells, plasma and brain tissue.

The relations between the concentrations of a drug in the blood (plasma, haemoglobin, red blood cells (RBCs), RBC membranes) and in the brain tissue (homogenate, membranes, cytosol) were investigated during chronic administration of imipramine. Radioimmunoassay was employed to measure the antidepressant concentrations. The concentrations were measured and analysed in 40 rats receiving various doses of imipramine. The concentration of total imipramine (imipramine + desipramine) in erythrocyte membranes (ghosts) amounted to 79.4 +/- 4.6% (mean +/- S.E.M., N = 40) of those measured in intact RBCs. Marked accumulation of the drug in the brain tissue, especially in brain cell membranes, was confirmed. The concentrations in brain tissue homogenate was found to be 14.8 times higher than that in RBCs. Values in brain membranes were 10.9 times higher than that in blood element membranes. There is a significant association between the concentrations measured in brain homogenate, the blood plasma and RBC membranes. Blood concentrations can be used to estimate imipramine concentrations in the brain.

Microbiological aspects of determination of trichloroacetic acid in soil.

Soils have been shown to possess a strong microbial trichloroacetic acid (TCA)-degrading activity. High TCA-degradation rate was also observed during soil extraction with water. For correct measurements of TCA levels in soil all TCA-degrading activities have to be inhibited immediately after sampling before analysis. We used rapid freezing of soil samples (optimally in liquid nitrogen) with subsequent storage and slow thawing before analysis as an efficient technique for suppressing the degradation. Frozen soil samples stored overnight at -20 degrees C and then thawed slowly exhibited very low residual TCA-degrading activity for several hours. Omitting the above procedure could lead to the confusing differences between the TCA levels previously reported in the literature.

Microbial chlorination of organic matter in forest soil: investigation using 36Cl-chloride and its methodology.

Chloride, which comes into the forest ecosystem largely from the sea as aerosol (and has been in the past assumed to be inert), causes chlorination of soil organic matter. Studies of the chlorination showed that the content of organically bound chlorine in temperate forest soils is higher than that of chloride, and various chlorinated compounds are produced. Our study of chlorination of organic matter in the fermentation horizon of forest soil using radioisotope 36Cl and tracer techniques shows that microbial chlorination clearly prevails over abiotic, chlorination of soil organic matter being enzymatically mediated and proportional to chloride content and time. Long-term (>100 days) chlorination leads to more stable chlorinated substances contained in the organic layer of forest soil (overtime; chlorine is bound progressively more firmly in humic acids) and volatile organochlorines are formed. Penetration of chloride into microorganisms can be documented by the freezing/thawing technique. Chloride absorption in microorganisms in soil and in litter residues in the fermentation horizon complicates the analysis of 36Cl-chlorinated soil. The results show that the analytical procedure used should be tested for every soil type under study.

[The effect of cocaine on binding of tricyclic antidepressives in the synaptic plasma membranes in the brain]. / Vliv kokainu na vazbu tricyklických antidepresiv v SPM mozku.

Effect of cocaine on binding of 3H-imipramine, 3H-desmethylimipramine, 3H-didesmethylimipramine and 3H-amitriptyline to brain synaptic plasma membranes (SPM) was studied. Binding of methylated tricyclic antidepressants was more affected. Cocaine inhibits 3H-imipramine binding at concentrations higher than 10(-5) mol/l. Binding stimulated by phosphatidylserine was affected more significantly.

Radioimmunoassay of dibenzazepines and dibenzcycloheptanodienes in body fluids and tissues.

In an attempt to establish a radioimmunoassay (RIA), imipramine and amitriptyline immunogens were prepared; desmethyl derivatives were converted into hemisuccinates, conjugated with bovine serum albumin and used for rabbit immunization. [3H]Amitriptyline (4.3 TBq/mmol) and [3H]imipramine (2.9 TBq/mmol) were prepared by catalytic dehalogenation or reductive alkylation. Dibenzazepines and dibenzcycloheptanodienes were determined in biological fluids by a direct method without deproteinization (lower detection limit of 0.5 microgram.l-1); using high-yield methods they were extracted from cell membranes. Assay of tricyclic antidepressants in humans showed that these substances disappear from plasma much earlier than from cell membranes. Dissociation of the antidepressants bound to cell membranes is slow and their plasma concentrations are not influenced by standing for 2 h at 4 degrees C. During preparing the membranes for binding studies these substances are not removed, and they may affect the results of the binding studies.

[Ca(2+)-channel blockers and binding of tricyclic antidepressive agents]. / Blokátory Ca(2+)-kanálu a vazba tricyklických antidepresív.

The interactions between Ca(2+)-channel blockers (verapamil and gallopamil) and synaptic plasma membranes (SPM) from bovine brain or human lymphocyte and platelet plasma membranes were studied. Changes in binding parameters of [3H]imipramine, [3H]desmethylimipramine and [3H]gallopamil were determined after addition of unlabelled verapamil or imipramine and after addition of phosphatidylserine (PS) (PS-stimulation). Specific binding of [3H]imipramine to SPM was decreased and [3H]desmethylimipramine binding was increased by 1 microM verapamil. [3H]gallopamil binds specifically to SPM as well as to platelet and lymphocyte membranes. [3H]gallopamil binding to SPM or lymphocyte plasma membranes was PS-stimulated in contrast to platelet plasma membranes without PS effect on binding. Imipramine inhibited both [3H]gallopamil binding and PS-stimulated [3H]gallopamil binding to SPM or lymphocyte plasma membranes. Mutual effects of tricyclic antidepressants and Ca(2+)-channel blockers on their binding sites require relatively high drug concentrations. Mechanism of Ca(2+)-channel blockers action in the treatment of depression may be connected rather with changes in signal transduction through serotonin and catecholamine receptor systems than with direct interaction of drugs with binding sites for tricyclic antidepressants.

In vivo metabolism of 2,6,9-trisubstituted purine-derived cyclin-dependent kinase inhibitor bohemine in mice: glucosidation as the principal metabolic route.

Synthetic cyclin-dependent kinase inhibitors have recently been referred to as effective antiproliferative agents. This study was conducted to characterize clearance of a 3H-labeled, trisubstituted purine-type inhibitor, 8-[3H]bohemine [6-benzylamino-2-(3-hydroxypropylamino)-9-isopropylpurine], in mice. Radioactivity profiles were analyzed by liquid scintillation counting and by thin layer chromatography followed by autoradiography. Metabolite structures were elucidated by mass spectrometry, NMR, and enzymatic analyses. Bohemine was rapidly and completely metabolized in vivo and disappeared from circulation during the first 60 min following intravenous administration. The metabolites were partly eliminated by the hepatobiliary tract and partly by renal excretion. The terminal hydroxyl group located at the C2 side chain of bohemine made the compound susceptible to main metabolic attacks, i.e., distinct types of conjugation reactions with glycosyl donors as well as an oxidative reaction. Other pathways were of relatively minor significance. Bohemine O-beta-D-glucoside was the most abundant metabolite to be excreted. The enzymatic mechanism responsible for bohemine glucosidation in vitro required the presence of a UDP-glucoside donor. Additional glycosidation products were observed after inclusion of UDP-glucuronide, UDP-xylose, UDP-galactose, or UDP-N-acetylglucosamine into microsomal incubates. Glycosidations occurred faster in the kidney incubates than in hepatic ones. The second principal bohemine metabolite was a carboxylic acid, 6-benzylamino-2-(2-carboxyethylamino)-9-isopropylpurine. A cytosolic, 4-methylpyrazole-sensitive alcohol dehydrogenase class I was shown to mediate oxidation of the terminal hydroxyl group of bohemine into this acid, which was the only metabolite found in the blood in significant amounts. However, it displayed only weak cyclin-dependent kinase-1-inhibitory activity (IC(50) > 100 microM) when compared with that of bohemine (IC(50) approximately 1 microM).