Structure- and Cation-Dependent Mechanism of Interaction of Tricyclic Antidepressants with NMDA Receptor According to Molecular Modeling Data

Some tricyclic antidepressants (TCAs), including amitriptyline (ATL), clomipramine (CLO), and desipramine (DES), are known to be effective for management of neuropathic pain. It was previously determined that ATL, CLO, and DES are capable of voltage-dependent blocking of NMDA receptors of glutamate (NMDAR), which play a key role in pathogenesis of neuropathic pain. Despite the similar structure of ATL, CLO, and DES, efficacy of their interaction with NMDAR varies significantly. In the study presented here, we applied molecular modeling methods to investigate the mechanism of binding of ATL, CLO, and DES to NMDAR and to identify structural features of the drugs that determine their inhibitory activity against NMDAR. Molecular docking of the studied TCAs into the NMDAR channel was performed. Conformational behavior of the obtained complexes in the lipid bilayer was simulated by the method of molecular dynamics (MD). A single binding site (upper) for the tertiary amines ATL and CLO and two binding sites (upper and lower) for the secondary amine DES were identified inside the NMDAR channel. The upper and lower binding sites are located along the channel axis at different distances from the extracellular side of the plasma membrane. MD simulation revealed that the position of DES in the lower site is stabilized only in the presence of sodium cation inside the NMDAR channel. DES binds more strongly to NMDAR compared to ATL and CLO due to simultaneous interaction of two hydrogen atoms of its cationic group with the asparagine residues of the ion pore of the receptor. This feature may be responsible for the stronger side effects of DES. It has been hypothesized that ATL binds to NMDAR less efficiently compared to DES and CLO due to its lower conformational mobility. The identified features of the structure- and cation-dependent mechanism of interaction between TCAs and NMDAR will help in the further development of effective and safe analgesic therapy.

Identification of hub genes and discovery of promising compounds in gastric cancer based on bioinformatics analysis

Aim: To explore the mechanism of gastric carcinogenesis by mining potential hub genes and to search for promising small-molecular compounds for gastric cancer (GC). Materials & methods: The microarray datasets were downloaded from Gene Expression Omnibus database and the genes and compounds were analyzed by bioinformatics-related tools and software. Results: Six hub genes (MKI67, PLK1, COL1A1, TPX2, COL1A2 and SPP1) related to the prognosis of GC were confirmed to be upregulated in GC and their high expression was correlated with poor overall survival rate in GC patients. In addition, eight candidate compounds with potential anti-GC activity were identified, among which resveratrol was closely correlated with six hub genes. Conclusion: Six hub genes identified in the present study may contribute to a more comprehensive understanding of the mechanism of gastric carcinogenesis and the predicted potential of resveratrol may provide valuable clues for the future development of targeted anti-GC inhibitors.

Insights from molecular dynamics: the binding site of cocaine in the dopamine transporter and permeation pathways of substrates in the leucine and dopamine transporters

The dopamine transporter (DAT) facilitates the regulation of synaptic neurotransmitter levels. As a target for therapeutic and illicit psycho-stimulant drugs like antidepressants and cocaine, DAT has been studied intensively. Despite a wealth of mutational and physiological data regarding DAT, the structure remains unsolved and details of the transport mechanism, binding sites and conformational changes remain debated. A bacterial homolog of DAT, the leucine transporter (LeuT(Aa)) has been used as a template and framework for modeling and understanding DAT. Free energy profiles obtained from Multi-Configuration Thermodynamic Integration simulations allowed us to correctly identify the primary and secondary binding pockets of LeuT(Aa). A comparison of free energy profiles for dopamine and cocaine in DAT suggests that the binding site of cocaine is located in a secondary pocket, not the primary substrate site. Two recurring primary pathways for intracellular substrate release from the primary pocket are identified in both transporters using the Random Acceleration Molecular Dynamics method. One pathway appears to follow transmembranes (TMs) 1a and 6b while the other pathway follows along TMs 6b and 8. Interestingly, we observe that a single sodium ion is co-transported with leucine during both simulation types.

Synthesis of some tropane derivatives of anticipated activity on the reuptake of norepinephrine and/or serotonin

A variety of tropane derivatives 14a-g were prepared via the reaction of the alcohol analogs 12a and 12b with substituted fluorobenzenes 13a-f. The prepared compounds were tested for their activity and selectivity toward the norepinephrine transporter (NET) and serotonin transporter (SERT) using yohimbine-induced mortality and 5-hydroxytryptophan-induced neurotoxicity in mice, respectively. All the tested compounds were found to be NE and 5-HT reuptake inhibitors except 14d which exhibited selective 5-HT reuptake inhibition activity.

CE of tricyclic antidepressant clomipramine and metabolites: Electromigration and wall adsorption

CE of tricyclic antidepressants clomipramine and its metabolites demethylclomipramine, didemethylclomipramine and 8-hydroxyclomipramine resulted in partly extremely tailing peaks in bare fused-silica capillaries. Especially at high pH of the BGE this behavior was not unexpected as adsorption of the cationic analytes onto the negatively charged wall due to electrostatic attraction can be supposed. Less expected was the observation that peak tailing could not be overcome neither by using a capillary with dynamic coating with cationic CTAB added to the BGE, nor by the usage of a capillary permanently coated with polyvinyl alcohol (PVA), both operated at acidic pH. As this tailing was even more pronounced than with bare fused silica, and was suppressed upon addition of MeCN to the BGE, another source of adsorption than pure ion-ion interaction seems plausible. In the bare silica capillary the mobility, mu, of the analytes followed roughly the pH dependence of a monoacidic base, but two deviations from the sigmoid theoretical curve were evident: (i) even at low pH the mobilities were not constant; they decreased in contrary with pH over the entire range; (ii) the apparent pK(a) values of two analytes, derived at the pH with halve the mobility at low pH, are significantly smaller than the thermodynamic pK(a). Upon modifying the expression for mu = f(pH), and considering the pH dependence of the negative charge density at the wall by an additional term which takes chromatographic retention into account, an equation was derived which enables the description of the observed electromigration of the analytes as function of pH, pK(a) of analytes and surface silanol groups, actual mobility of analytes, distribution coefficient (or retention factor) due to adsorption including its pH dependence. The interplay of electrophoretic movement and residual adsorptive retention allowed to resolve the analytes finally in an uncoated capillary, namely at pH 7.65 (30 mM ionic strength), whereas at the cost of the robustness of the separation system.

Isolation and identification of the photodegradation products of the photosensitizing antidepressant drug clomipramine. Phototoxicity studies on erythrocytes

The isolation and identification of the photodegradation products of clomipramine (CIP) in phosphate buffered saline (PBS pH 7.4 and 6.0) solution and methanol under aerobic conditions were studied. Six compounds were identified and four of them were isolated and characterized by spectroscopic methods. A radical mechanism with the participation of the solvent is proposed for the photodegradation of CIP which undergoes homolytic cleavage of the carbon-chlorine bond and also photooxidation of the amine group. CIP was able to induce photohemolysis when it was irradiated in PBS pH 7.4 and in PBS pH 6.0 containing a suspension of human red blood cells (RBCs). The photohemolysis experiments in the presence of additives DABCO and GSH showed nearly total inhibition of drug-induced photohemolysis. The efficient inhibition of photohemolysis by the radical scavenger GSH compared with the inhibition show by DABCO suggests a moderate effect by singlet oxygen. Clomipramine-N-oxide was the unique photoproduct able to induce hemolysis and photohemolysis when it was incubated and irradiated with RBCs for 1 h. A mechanism involving singlet oxygen, radicals and photoproducts is suggested for the reported phototoxicity.

Synthesis and antidepressant activities of some 3,5-diphenyl-2-pyrazolines

Ten new 3,5-diphenyl-2-pyrazoline derivatives were synthesised by reacting 1,3-diphenyl-2-propen-1-one with hydrazine hydrate. The chemical structures of the compounds were proved by means of their IR, 1H-NMR spectroscopic data and microanalyses. The antidepressant activities of these compounds were evaluated by the 'Porsolt Behavioural Despair Test' on Swiss-Webster mice. 3-(4-Methoxyphenyl)-5-(3,4-dimethoxyphenyl)-2-pyrazoline, 3-(4-methoxyphenyl)-5-(2-chloro-3,4-dimethoxyphenyl)-2-pyrazoline and 3-(4-chlorophenyl)-5-(2-chloro-3,4-dimethoxyphenyl)-2-pyrazoline reduced 41.94-48.62% immobility times at 100 mgkg(-1) dose level. In addition, it was found that 4-methoxy and 4-chloro substituents on the phenyl ring at position 3 of the pyrazoline ring increased the antidepressant activity; the replacement of these groups by bromo and methyl substituents decreased activity in mice.

Radiopacity of clomipramine conglomerations and unsuccessful endoscopy: report of 4 cases

BACKGROUND

The radiopacity of ingested substances may serve as a clue to the presence of particular compounds, as this characteristic varies considerably among medications and household products. Tablet conglomerations are also variably radiopaque. We report 4 cases of clomipramine poisoning associated with formation of radiopaque masses, believed to be clomipramine, in the area of the stomach.

CASE REPORTS

Four patients were admitted to the Toxicological Intensive Care Unit after ingestions of, respectively, 8.5 g (180 tablets of mixed strength), 7.5 g (100 tablets), 10.5 g (140 tablets), and 4.5 g (60 tablets) of clomipramine, along with other sedatives and antipsychotics. In each case, a rounded density was observed in the gastric area on plain chest radiograph. The hospital courses of each patient were marked by tachycardia, hypotension, QRS and QT prolongation, seizures, and decreased mental status. Three of 4 patients underwent unsuccessful endoscopy to remove tablet fragments and subsequently suffered gastrointestinal hemorrhage requiring transfusion. All patients were discharged recovered from the hospital.

DISCUSSION

Clomipramine, a potent tricyclic antidepressant, has been previously reported to be nonradiopaque, and has not been reported to induce formation of concretions. These cases suggest that massive ingestions of clomipramine may form bezoars which are radiopaque and may be associated with serious toxicity. Careful consideration should be given prior to the use of gastric endoscopy for the retrieval of tablet fragments since significant hemorrhage, attributed to the procedure itself rather than to clomipramine toxicity, may ensue.

Membrane permeation by multidrug-resistance-modulators and non-modulators: effects of hydrophobicity and electric charge

This study was designed to test the hypothesis that lipophilic cationic drugs with only roughly similar structures mediate the reversal of multidrug-resistance (MDR) by interacting with membrane phospholipids. The permeation properties of MDR-modulators and non-modulators were studied by quantifying their ability to induce the leakage of Sulphan blue through the membrane of negatively charged unilamellar liposomes. Of the 22 compounds under investigation, only those bearing a net positive electric charge per molecule (z) > or = 0.2 induced dye leakage. All these efficient drugs are well-known MDR-modulators: calcium-channel blockers (propranolol, verapamil, diltiazem and dipyridamole), calmodulin antagonists (clomipramine and thioridazine) and antiparasitic agents (mepacrine, thioacridine derivatives and quinine). The non-modulators tested, including antineoplastic agents and steroids, did not induce any membrane permeation. The permeation process was a co-operative one (1.1 < Hill coefficient < 4.1) and the permeation doses inducing 50% dye leakage (PD50) were 1.9-11.2 mM. The permeation ability of the MDR-modulators (log(1/PD50)) increased significantly with octanol-buffer distributions per unit net electric charge ((logD)/z). The results provide evidence that a complex interplay occurs between the electric charge and the lipophilicity of the MDR-modulators when a dye leakage is induced through model membranes, and probably also when the MDR is reversed in leukaemic cells.

Comparative study of the sorption of clomipramine and viloxazine hydrochlorides in Stedim 6 and PVC bags

The stability of two antidepressant drugs, clomipramine and viloxazine hydrochlorides, was studied as was their possible sorption on Stedim 6, a new multilayer polyethylene-lined film, which was considered comparatively to polyvinyl chloride (PVC) and glass surfaces. Appropriate amounts of the drugs were added to 500 ml of 5% dextrose and 0.9% sodium chloride solutions in Stedim 6 and PVC bags, and in glass flasks, in order to obtain the concentrations currently used in clinical practice. All the containers were stored at room temperature in daylight for 72 hours. Samples were taken at various times and evaluated for remaining drug concentrations by UV spectrometry. The two drugs appeared stable under the given conditions. No concentration decrease was observed in glass flasks. Viloxazine hydrochloride showed an excellent compatibility with the PVC bags, but a slight concentration decrease (about 6-7% in 72 hours) was observed for clomipramine hydrochloride, depending on the contact duration. The compatibility of the two drugs with the new material Stedim 6 was found to be perfect. The behavioral differences observed between the two drugs with regard to PVC are explained in terms of differences of lipophilicity of the drugs. Those observed for a given drug with regard to the two materials are due to the crystalline structure of polyethylene and the amorphous one of PVC.

Polyelectrolyte/amphiphile interaction studied by surface tension measurements

The interaction of kappa-carrageenan with three positively charged drug molecules with amphiphile character has been examined using surface tension measurements. The surface tension was measured by the pendant drop method which makes possible the determination at an apparent steady state which is important for polymeric systems. The results are compared with adsorption isotherms from dialysis equilibrium. The surface tension data, show that the presence of kappa-carrageenan in the amphiphile solutions leads to an increased and pronounced lowering of the surface tension in a low concentration range of amphiphile. It is also shown that not only the hydrophobicity of the amphiphile but also the structure of the polyelectrolyte (charge density and helix-coil structure) largely determine the extent of interaction.

Spectroscopic analysis of charge transfer complex formation and peroxidase inhibition with tricyclic antidepressant drugs: potential anti-thyroid action

Inspection of the chemical structures of tricyclic antidepressant drugs indicates that they might interfere with the synthesis of thyroid hormones. This iatrogenic potential was demonstrated in vitro by the spectrophotometric detection in both the visible and UV regions of the formation of a complex between antidepressants and iodine. The values of Kc, the formation constant of the drug-iodine complex, were calculated. The concentration of antidepressant which led to a 50% inhibition (IC50) of horseradish peroxidase was also determined. The anti-thyroid activity of drugs can be evaluated from these two parameters, Kc and IC50. The results were compared to those obtained with methimazole, a reference anti-thyroid agent. Antidepressants derived from imipramine appeared to have anti-thyroid activity. This result is now awaiting confirmation in animal experiments.

Interactions between six psychotherapeutic drugs and plastic containers. Influence of plastic material and infusion solutions

The interactions of chlorpromazine, clomipramine, maprotiline and viloxazine hydrochlorides, and of clorazepate dipotassium salt and diazepam with polyvinyl chloride (PVC) and Stedim 6 infusion bags were studied. Stedim 6, is anew multilayer film whose inner layer is made of polyethylene. The drugs were in 5% dextrose and 0.9% sodium chloride isotonic solutions and the influence of these was also considered. The remaining concentrations of each drug were determined at regular time intervals in a 24-h period, by a spectrofluorometric method for chlorpromazine hydrochloride and by ultraviolet spectrophotometric methods for the other drugs. No binding was observed for viloxazine and maprotiline hydrochlorides whatever the infusion solution and the plastic container. A slight retention in PVC bags, but not in Stedim 6 ones, was noted for clomipramine hydrochloride and clorazepate dipotassium salt. This was more marked in the sodium chloride solution than in the dextrose one. Diazepam and chlorpromazine hydrochloride were bound both in PVC and Stedim 6 bags, but more in the former and more again in the sodium chloride solution than in the dextrose one. The results were explained in terms of the degree of crystallinity of the plastic material and the degree of lipophilicity of the drugs. Practical consequences are discussed.

Comparative sorption of clomipramine, viloxazine, and maprotiline hydrochlorides in polyvinylchloride bags and glass vials

The sorption of clomipramine, viloxazine, and maprotiline hydrochlorides was studied comparatively in polyvinylchloride (PVC) bags and glass flasks for up to 72 hours. When stored in glass flasks, no decrease in concentration was observed for any of the three drugs, either in dextrose or sodium chloride isotonic solution. When stored in PVC bags, a slight loss (about 7% within 72 hours), was noted for clomipramine hydrochloride in both isotonic solutions, but not for the other two drugs.

A case of photosensitivity and contact allergy to systemic tricyclic drugs, with unusual features

A 43-year-old farmer on tricyclic antidepressive drugs developed a severe photodermatitis with associated liver involvement. The lesions spread to covered areas of the skin, suggesting photoallergy clinically. Patch and photopatch testing revealed photoallergy and contact allergy to clomipramine and contact allergy also to carbamazepine. In addition, the patient had positive patch test reactions to chlorpromazine, balsam of Peru and fragrance-mix, as well as a positive photopatch test to fentichlor. UVA and UVB erythema thresholds were normal. In this patient, an initial episode of photosensitization, probably elicited by clomipramine, was accompanied by contact allergy to this drug and to carbamazepine. The contact sensitivity to clomipramine could also be elicited by oral provocation without UV light. Hypothetically, a photoproduct of clomipramine may have been the original sensitizer, this compound subsequently cross-reacting with clomipramine and, possibly with carbamazepine.