Relationships among dopamine transporter affinities and cocaine-like discriminative-stimulus effects.

RATIONALE: The discriminative-stimulus effects of cocaine have been reported to be mediated by indirect agonist actions initiated by the blockade of dopamine uptake, and the potencies of drugs that have discriminative-stimulus effects like cocaine are directly related to their dopamine transporter binding affinities. The binding to the dopamine transporter by cocaine and many of its analogs has been reported to fit better using a two-site model than a one-site model. OBJECTIVES: The present study examined the relationship among binding affinities of dopamine uptake inhibitors at these two sites and their potencies to produce discriminative-stimulus effects. METHODS: The inhibition constants (K(i) values) were derived for unlabeled dopamine uptake inhibitors for displacement of [(3)H]WIN 35,428 from rat caudate putamen membranes. These K(i) values were related to the ED(50) values obtained in rats trained to discriminate 10 mg/kg cocaine from saline injections under a fixed-ratio 20 schedule of food reinforcement. RESULTS: Among the dopamine uptake inhibitors studied, the binding data for eight compounds (WIN 35,428, nomifensine, WIN 35,981, WIN 35,065-2, methylphenidate, cocaine, cocaethylene, and bupropion) were better fit by a two-site model than a one-site model. The data for the remaining eleven compounds (RTI-31, RTI-55, RTI-121, RTI-32, LU19-005, BTCP, GBR12909, GBR12935, mazindol, LU17-133, and EXP561) were better fit by a one-site model. Of the drugs that were fit best by a two-site model, there was a higher correlation among the K(i) values for the high-affinity site and the ED(50) values (R(2)=0.655; P=0.015) than there was for the low-affinity site (R(2)=0.543; P=0. 037). Of the remaining drugs, there was a high correlation among the K(i) values and the ED(50) values for the discriminative-stimulus effects (R(2)=0.523; P=0.012). CONCLUSIONS: These data suggest that the discriminative-stimulus effects of cocaine are more closely related to actions mediated by high-affinity binding to the dopamine transporter than they are to actions mediated by the low-affinity site. The further assessment of the respective contributions of high- and low-affinity binding to the behavioral effects of cocaine will be greatly enhanced with the development of pharmacological tools that have a high degree of selectivity for one of these components.

Influence of thiols on the chlorinating effect of a myeloperoxidase system.

The structure-activity relationships for the interactions of a number of sulfhydryl compounds on the transformation of (Z)-3-(4-bromophenyl)-3-(3-pyridyl)allylamine (CPP 200) by an MPO-H2O2-Cl-(-)system at pH 5.25 have been studied. It was found that the inhibitory effect of the thiol group was strongly dependent on the presence of an electron-withdrawing NH3(+)-group in the molecule. Also, the acid-base properties of the thiolic compounds were involved in the inhibitory mechanisms.

(Z)-3-(4-bromophenyl)-3-(3-pyridyl)allylamine as substrate for studies of myeloperoxidase activity.

(Z)-3-(4-Bromophenyl)-3-(3-pyridyl)allylamine (CPP 200) is transformed to the corresponding chloroimine by hypochlorite ion (ClO-) formed in the presence of myeloperoxidase. A scheme for this transformation is given. The influence of various compounds on this process has been studied. Cysteamine, cysteine and 6-chloro-3-hydrazino-pyridazine inhibited the transformation of CPP 200, while some p-hydroxyphenyl derivatives increased the rate of transformation of CPP 200. The increase seen on addition of the p-hydroxyphenyl derivatives is not a chloride-dependent reaction. Various mechanisms for the inhibiting effect as well as for the activating effect on the transformation of CPP 200 are discussed.

Effects of zimeldine and its metabolites, clomipramine, imipramine and maprotiline in experimental allergic neuritis in Lewis rats.

The influence of the selective serotonin (5-HT) reuptake inhibiting antidepressant zimeldine and its metabolite norzimeldine was tested on experimental allergic neuritis (EAN) in Lewis rats, which is an animal model of the Guillain-Barré syndrome (GBS) in man. Zimeldine and norzimeldine both suppressed clinical signs of actively induced EAN when given at a dose of 20 mg/kg/day intraperitoneally via osmotic pumps. The effects of zimeldine, its metabolites norzimeldine and CPP 200 as well as of the antidepressants clomipramine, imipramine and maprotiline on in vitro immune response were tested. Thereby we used an immunospot assay for interferon-gamma (IFN-gamma) produced by lymph node mononuclear cells (MNC), which reflects number of memory T lymphocytes activated by antigen or lectin, in this experiment bovine peripheral nerve myelin (BPM) and phytohemagglutinin (PHA), respectively. In the IFN-gamma secretion assay zimeldine, CPP 200, clomipramine and maprotiline all in a concentration-dependent mode reduced the number of IFN-gamma secreting cells while norzimeldine and imipramine did not affect the IFN-gamma secretion. In assays for proliferation in response to antigen or lectin, the concentration 10(-4) M was judged toxic for all substances tested, and at concentrations below that all but zimeldine showed a dose-dependent slight reduction of MNC proliferation. The action of several drugs on induced T cell secretion of IFN-gamma suggests that the mechanisms for the suppressive effect of zimeldine and norzimeldine on EAN symptoms can be due to an action on myelin T cell autoreactivity. All the monoamine reuptake inhibiting antidepressants tested in this study showed immunomodulatory effects by either a reduction of the number of IFN-gamma-secreting cells or the MNC proliferation. These observations call for further studies of immunological mechanisms in the pathogenesis of mental disorders as well as on the potential role of drugs acting on the monoamine systems in the treatment of recognized autoimmune diseases.

Oxidation of N-hydroxynorzimeldine to a stable nitrone by hepatic monooxygenases.

Liver microsomes from uninduced hogs catalyzed the NADPH-dependent N-oxidation of the hydroxylamine (Z)-3-(4-bromophenyl)-N-hydroxy-N-methyl-3-(3-pyridyl)allylamine. The conjugated nitrone N-[(2Z)-3-(4-bromophenyl)-3-(3-pyridyl)-2-propenylidene]methylamin e N-oxide was the principal product and accounted for 90-95% of the total hydroxylamine metabolized by microsomes. The nitrone had a relatively high chemical stability which was investigated at various conditions. Studies of the biochemical mechanisms for N-oxidation of N-hydroxy-norzimeldine showed that the reaction was catalyzed by the flavin-containing monooxygenase. This conclusion was based on studies with the purified hog liver flavin-containing monooxygenase and hog liver microsomes. Purified rat liver cytochrome P-450IIB-1 was ineffective at catalyzing N-oxidation of N-hydroxynorzimeldine.

Stereoselective N-oxygenation of zimeldine and homozimeldine by the flavin-containing monooxygenase.

The metabolism of (Z)- and (E)-zimeldine and (Z)- and (E)-homozimeldine in hepatic rat and hog microsomes is described. The major metabolite observed in all cases examined was the tertiary amine N-oxide and it was formed at a rate 7-20 times that of norzimeldine or homonorzimeldine. N-Oxygenation requires NADPH and is stimulated by n-octylamine. Thiobenzamide and methimazole significantly inhibit N-oxide formation whereas heat pretreatment of microsomes completely abolishes N-oxide formation, strongly suggesting that zimeldine N-oxygenation if solely dependent on the flavin-containing monooxygenase. Hog liver microsomes N-oxygenate the Z-allylic and homoallylic tertiary amines in marked preference to the E-isomers, whereas rat liver microsomes N-oxygenate E-isomers to a greater extent than Z-isomers. Thus, opposite stereoselectivity for zimeldine N-oxygenation occurs in rat liver and hog liver microsomes.

Quantitative autoradiography of serotonin uptake sites in rat brain using [3H]cyanoimipramine.

The binding of [3H]cyanoimipramine to serotonin uptake sites in rat brain slices was studied using quantitative autoradiography. Binding was of high affinity and was to a single class of binding site. This is in contrast to results previously obtained by others with [3H]imipramine where two binding sites were observed. The sites labeled by [3H]cyanoimipramine had properties consistent with this ligand labeling serotonin uptake sites, as: (1) binding is displaced by drugs which are potent inhibitors of serotonin uptake but not by drugs which are weak inhibitors of uptake; (2) binding is dependent on the presence of sodium ions as is the uptake of serotonin; (3) binding is almost completely eliminated in the brains of rats lesioned by the serotonin neurotoxin 5,7-dihydroxytryptamine; (4) the distribution of binding sites throughout the rat brain is highly correlated with that found previously for [3H]indalpine, a potent serotonin uptake inhibitor, and for [3H]imipramine. The properties of binding of [3H]cyanoimipramine make it an ideal ligand for the quantitative autoradiography of serotonin uptake sites.

Trichloroethylene inhibits uptake of 3H-5-hydroxytryptamine but not uptake of 3H-zimeldine or 3H-propranolol in isolated perfused rat lungs.

Pulmonary uptake of 5-hydroxytryptamine (5-HT), zimeldine and propranolol were studied using the isolated perfused rat lung model. The 5-HT uptake was found to be attenuated by approximately 50 per cent in comparison to the control, when the lungs were ventilated with air containing 5,000 p.p.m. trichloroethylene. In experiments in which the active uptake of 5-HT was blocked with the selective 5-HT uptake inhibitor zimeldine (5 X 10(-6) M), the uptake of 5-HT decreased by 70 +/- 1.7 per cent (mean +/- S.E.M.). When trichloroethylene (5,000 p.p.m. and 18,000 p.p.m.) was added, no further decrease in uptake was noted. The uptake of 3H-zimeldine (10(-6) M) and 3H-propranolol (10(-6) M) was unaffected by ventilating the lungs with trichloroethylene. It is concluded that trichloroethylene inhibits the active uptake of 5-HT from the pulmonary circulation, but that it has no effect on the uptake of zimeldine or propranolol, which are taken up predominantly by passive diffusion.

Effects of age on antidepressant kinetics and memory in Fischer 344 rats.

Experiments were conducted in young (3-4 months) and old (24-25 months) male Fischer 344 rats to assess the effects of amitriptyline, scopolamine, and zimelidine on short term memory using an eight arm radial maze paradigm. Kinetic analyses employing serial blood sampling were also conducted for amitriptyline and zimelidine in an attempt to determine if age-related deficits in performance could be related to changes in pharmacokinetics. In the maze, acquisition of performance was significantly decreased in old rats compared to young. Amitriptyline (5 mg/kg) produced a significant decrement in maze performance on day four of a five day testing period in both young and old rats, while scopolamine (1 mg/kg) produced an initial decrement on day one, followed by a return towards pre-treatment levels in these two age groups. Zimelidine (5 mg/kg) produced no performance decrement in either young or old rats. Kinetic analyses revealed an increased half-life, slower plasma clearance, and a larger volume of distribution of amitriptyline and zimelidine in old rats. Although the kinetic parameters in aged rats exhibited a change in the direction of a decreased ability to metabolize both drugs, this change was not of sufficient magnitude to produce an additive detrimental effect on maze performance.

Long-term effects of two principally different antidepressant drugs on saliva secretion and composition.

In a double-blind, controlled, cross-over trial on 10 healthy volunteers, the effects of daily doses of maprotiline (75 mg) and zimelidine (100 mg) over a 14-day period were tested on saliva secretion rate and saliva composition. Based on current knowledge of salivary gland physiology and the difference in specificity between the two drugs, differences in salivary gland response could be expected. Since both drugs have anticholinergic effects which influence saliva secretion rate, the measured component concentrations had to be recalculated with regard to dependencies of secretion rate. Maprotiline, but not zimelidine, caused strong inhibition of secretion rate and accommodation ability. Maprotiline consistently caused around 50% increases in concentrations of the following saliva components: protein, amylase, fucose, hexose, sialic acid and potassium. The effects of zimelidine were less pronounced and resulted in initial increases of most organic components. 14 and 18 h after the intake of the drug these increases had disappeared and some of the components instead showed decreased concentrations. The results are consistent with current theories about facilitated serotoninergic and noradrenergic transmissions during treatment with antidepressants.

Pharmacokinetics of zimeldine in male alcoholics.

The pharmacokinetics of zimeldine, a 5-HT reuptake blocker with antidepressive effects, was studied after a single oral dose and after multiple oral administration in 19 alcoholic males, 10 with and 9 without chronic liver damage. The average plasma concentration of zimeldine as assessed by the AUC values (area under the plasma concentration-time curve) was significantly higher in the chronically liver damaged patients than in the patients without chronic liver damage. The plasma half-life of zimeldine was also significantly longer in the chronically liver damaged patients. There were no differences in the obtained pharmacokinetic parameters between the patients having nonchronic liver damage and healthy control subjects. The pharmacokinetics of the active metabolite norzimeldine (resulting from N-demethylation of zimeldine) showed no differences between the two groups of alcoholics and the healthy controls. The IgA values were significantly correlated to both the AUC and plasma half-life of zimeldine. No other correlation between clinical chemistry parameters and pharmacokinetic parameters of zimeldine and norzimeldine were found.

Single-site model of the neuronal 5-hydroxytryptamine uptake and imipramine-binding site.

Recently, a high affinity [3H]imipramine-binding site of protein nature that appeared to be related to the 5-hydroxytryptamine (5-HT, serotonin) uptake mechanism was demonstrated. This binding site was only part of desipramine-displaceable [3H]imipramine binding, which contained a significant amount of additional binding not related to 5-HT uptake. The present study further investigates the [3H]imipramine-binding site of protein nature in the rat brain. Displacement by 5-HT and 6-methoxytetrahydro-beta-carboline (6-MeO-TH beta C) revealed monophasic displacement patterns with 60% displaceable binding. This binding fraction was abolished by protease treatment of the brain tissue prior to binding assay. Saturation studies of [3H]imipramine binding (1-30 nM) in rat cortex showed that the binding displaced by 30 microM 5-HT [Bmax 322 +/- 16 fmol/mg of protein, Kd 4.17 +/- 1.07 nM (means +/- SE)] was not different from the binding displaced by 1.0 microM norzimeldine (Bmax 349 +/- 15 fmol/mg of protein, Kd 4.47 +/- 1.07 nM) or 30 microM 6-MeO-TH beta C (Bmax 439 +/- 28 fmol/mg of protein, Kd 5.49 +/- 1.09 nM). When 100 microM desipramine was used in saturation studies, the binding was different from that displaced by 5-HT with Bmax 608 +/- 42 fmol/mg of protein and Kd 6.68 +/- 1.09 nM. Both displacement and saturation studies in which two displacing agents were combined indicated that most of the binding competed by 5-HT (30 microM) and norzimeldine (1.0 microM) is identical. Similarly, the binding displaced by 5-HT or norzimeldine is subsumed within 6-MeO-TH beta C (30 microM)-displaceable binding. Lesion studies with parachloroamphetamine, a selective toxin for 5-HT terminals, which resulted in a 83% reduction of [3H] 5-HT uptake ( [3H]noradrenaline uptake unaffected), abolished cortical [3H]imipramine binding displaced by 30 microM 5-HT or 1.0 microM norzimeldine. (greater than 80% reduction). However, with 100 microM desipramine as displacer, 40% of the binding remained in lesioned animals. The [3H]imipramine binding displaced by 30 microM 5-HT or 1.0 microM norzimeldine was sodium dependent, and an increase in NaCl concentration from 0 to 120 mM resulted in a 10-fold increase in affinity without effect on Bmax, whereas no change in binding was observed with increasing concentrations of LiCl.(ABSTRACT TRUNCATED AT 400 WORDS)

Extrapyramidal signs following zimelidine overdose.

A 35-year-old woman with depression attempted suicide by taking an overdose of zimelidine (5 g), which was confirmed by zimelidine and norzimelidine plasma levels. Physical examination and repeat EKGs performed 2, 6, 9, and 12 hours later showed no alteration in her level of consciousness and only a slight increase in QT duration. However, the patient exhibited a distinct extrapyramidal syndrome, a finding consistent with animal data suggesting that zimelidine may possess some dopamine-receptor blockade properties.

Influence of renal failure on the kinetics of zimeldine and norzimelidine.

The kinetics of zimeldine (Z) and its demethylated metabolite, norzimelidine (NZ), were determined after administration of a single 200 mg oral dose of Z to 6 healthy volunteers (Group I), and to patients with mild (Group II) and severe renal failure (Group III). Z and NZ concentrations were assayed by HPLC in serial plasma and urine samples over 6 days following the dose. In Group I Z was rapidly absorbed and metabolized into NZ, and then the plasma concentrations declined with apparent elimination half-lives of 8.4 h and 24.9 h for Z and NZ respectively, whilst the renal clearance of both compounds was low, Z 15.7 ml/min and NZ 33.0 ml/min. The plasma level of Z differed little between Groups I and III, but the area under the curve was significantly higher in Group III than in Group I subjects (AUC0-144 = 17.3 and 6.8 mumol X l-1 X h, respectively). Severe renal failure did not affect the peak plasma concentration of NZ but it did significantly increase peak time, apparent elimination half-life, and the area under the plasma concentration curve. A significant inverse relationship was found between renal clearance of NZ and plasma creatinine. Since NZ is as pharmacologically potent as Z, the results suggest that the dose of Z should be reduced in patients with severe renal insufficiency.

Zimelidine distribution in a sudden death.

The occurrence of zimelidine, a new experimental antidepressant, in a sudden death is presented. Tissues were extracted with n-butyl chloride. Quantitation was done by capillary gas chromatography with a nitrogen/phosphorus detector. Drug confirmation was obtained by gas chromatography and mass spectrometry. Blood concentrations of zimelidine and its metabolite norzimelidine were 0.71 and 2.2 mg/L respectively. Concentrations of the drug and metabolite are also given for the urine, liver, bile, and brain.

Acute kinetic and dynamic interactions of zimelidine with ethanol.

The acute interaction of zimelidine (Z) with ethanol (E) was examined in six healthy men aged 20 to 37 yr who randomly received each of four treatments 1 wk apart: Z, 200 mg by mouth, preceded by 1 hr and followed for 7 hr of oral E in juice dosed to maintain blood alcohol concentrations between 800 and 1000 mg/l; placebo Z and E; Z and juice; and placebo Z and juice. E decreased the rate of biotransformation of Z to norzimelidine (NZ) by 46%, but the AUCs of Z, NZ, and their total concentration over 8 hr were not altered by E. Acetaldehyde concentrations did not change and no aversive alcohol-sensitizing reaction was detected. E-induced impairments in memory, body sway, and a manual tracking task were further enhanced by Z, as was the E-induced decrease in friendliness. Data suggest Z and E interact kinetically and dynamically and suggest a mechanism whereby Z may decrease E intake in man.

Characterization of the binding of 3H-norzimeldine, a 5-HT uptake inhibitor, to rat brain homogenates.

The binding of radiolabelled norzimeldine, a potent selective 5-HT reuptake inhibitor, to rat brain homogenates is described. 3H-Norzimeldine binds to a site with high affinity (KD = 10.5 nM) in a saturable manner (Bmax = 15.4 pmol/g wet weight in the cerebral cortex). The number of binding sites in the various regions of the brain parallels the capacity of the 5-HT reuptake mechanism. Drugs that inhibit the reuptake of 5-HT are also potent inhibitors of the 3H-norzimeldine binding, as are the tricyclic antidepressants, which are non-specific inhibitors of the noradrenaline and the 5-HT reuptake. Lesioning experiments using DSP4 (a NA neurotoxin) and p-chloroamphetamine (a 5-HT neurotoxin) suggest that the binding site is located on the presynaptic 5-HT nerve terminal, although a small component of the binding may be to noradrenergic uptake sites as well.

Effects of antidepressant drugs on histamine-H1 receptors in the brain.

The histamine-H1 receptor blocking properties of a number of structurally different antidepressant drugs have been evaluated using a 3H-mepyramine binding assay and a guinea-pig ileum preparation. The tricyclic antidepressants all inhibited the histamine-H1 receptor. Some newer antidepressant drugs, such as zimelidine and nomifensine were devoid of activity while others, such as iprindole and mianserin were very potent. It is concluded that antagonistic effects on the histamine-H1 receptor is not associated with the therapeutic efficacy in depression, but may contribute to the sedative effects of the antidepressant drugs.

Pharmacokinetic study of zimelidine using a new GLC method.

A specific, sensitive, rapid and reproducible analytical method for zimelidine [3-(4-bromophenyl)-N,N-dimethyl-3(3-pyridyl)allylamine] and its biologically active demethylated metabolite, norzimelidine, in human plasma was developed using gas-liquid chromatography (GLC) with loxapine as the internal standard. A good separation of zimelidine and norzimelidine was obtained following derivatisation of norzimelidine with heptafluorobutyric anhydride, the retention times being 6.16 and 10.35 minutes, respectively. The sensitivity of the method is 5 ng/ml for zimelidine and norzimelidine. Plasma concentrations of zimelidine and norzimelidine were determined in 10 healthy volunteers following the administration of a single oral dose of 100mg zimelidine. Zimelidine was rapidly absorbed, giving a mean peak plasma concentration of 103.9 +/- 34.8 ng/ml. The mean plasma elimination half-life was 8.4 +/- 2.0 hours for zimelidine and 19.4 +/- 3.6 hours for norzimelidine. After long term administration of zimelidine (100mg bid for the first week, 100mg tid for the second week and 100mg am and 200mg pm for the third and fourth weeks) to 2 depressed patients, plasma concentrations of norzimelidine were 2 to 4 times higher than those of zimelidine.