Electrocardiographic dose-dependent changes in prophylactic doses of dosulepine,lithium and citalopram

Tricyclic antidepressant drugs dosulepine (TCA), serotonin selective reuptake inhibitor (SSRI) and prophylactic agent with antidepressant effect lithium carbonicum (Li) have different cardiovascular side-effects. We compared them in the prophylactic therapy of periodic affective disorder in remission with TCA, SSRI and Li. Our previous papers confirmed the most prominent effects of heart electric field parameters in TCA patients (Slavícek et al., 1998). In the present work we studied for the first time the dose-dependent changes of ECG, body surface potential maps (BSPM - parameter DIAM 30, 40) in 43 TCA dosulepine, 40 SSRI citalopram and 30 Li outpatients (Hamilton scale: HAMD?10; age 40+/-5 years; treated for depressive disorders or bipolar disorders). The daily doses of dosulepine were 50-250 mg, citalopram 20-80 mg, Li plasma levels 0.66+/-0.08 meq/l. The electrocardiogram (ECG), vectorcardiogram (VCG), and BSPM were measured and calculated by the Cardiag 112.1 diagnostic system. The results have shown a relation between the dose of dosulepine and extremum (maximum and minimum) of depolarization isoarea map in dosulepine, but not in citalopram patients. The repolarization BSPM changes were most pronounced in SSRI patients. Lithium in long-term prophylaxy (1-22 years) caused only minimal ECG BSPM changes. The present results correspond with our previous observations.     

Enhancement of antidepressant potency by a potentiator of AMPA receptors

1. AMPA receptor potentiators (ARPs) exhibit antidepressant-like activity in preclinical tests (for example, the forced swim test) that are highly predictive of efficacy in humans. Unlike most currently used antidepressants, ARPs do not elevate extracellular levels of biogenic amines (e.g., 5HT, NE) in prefrontal cortex at doses that are active in the forced swim test.2. The present series of experiments examined the effects of combining the ARP, LY 392098, with biogenic amine-based antidepressants in the forced swim test. Male, NIH Swiss mice were placed in a cylinder of water and observed for attempted escape behaviors and immobility.3. LY 392098 dose-dependently decreased immobility as did a range of classical antidepressants. At doses of LY 392098 below those that decreased immobility, this compound significantly increased the potency with which fluoxetine and citalopram (SSRI antidepressants), imipramine (tricyclic antidepressant), duoxetine (norepinephrine/serotonin uptake blocker), nisoxetine (norepinephrine uptake inhibitor), and rolipram (PDE4 inhibitor) decreased immobility in the forced swim test with potency shifts upward of 5-fold (fluoxetine, imipramine, and rolipram). Likewise, ineffective doses of the traditional antidepressants potentiated the effects LY 392098 with shifts in the dose-effect functions that were 10-fold or more for citalopram, fluoxetine, imipramine, and duloxetine.4. Combined with other evidence for a role of AMPA receptors in the efficacy of antidepressants, the current data suggest that the addition of an ARP may augment the activity and perhaps the onset of the therapeutic effects of biogenic amine and second messenger-based antidepressants.     

Citalopram inhibits L-type calcium channel current in rat cardiomyocytes in culture

Selective serotonine reuptake inhibitors (SSRI) are believed to be less dangerous in the treatment of depressive disorder in comparison with tricyclic antidepressants (TCA) due to their relative lack of cardiotoxicity. Thus, we investigated the effect of citalopram (SSRI) on membrane electrophysiology in rat cardiomyocytes in tissue culture. The results were compared with those from amitriptyline (TCA). The whole-cell configuration patch-clamp technique was used. Both citalopram and amitriptyline exhibited the concentration-dependent inhibition of the L-type calcium channel current (ICa). Citalopram in concentrations of 3 microM and 10 microM inhibited peak calcium current by 2.7% and 8%, respectively. We demonstrated the same potency of citalopram and amitriptyline to inhibit ICa. These observations led us to conclude that citalopram and amitriptyline are drugs, which exhibit a similar potency for causing concentration-dependent inhibition of ICa.     

Alterations in serum and brain trace element levels after antidepressant treatment

We have studied the effect of chronic treatment with imipramine, citalopram and electroconvulsive shock (ECS) on serum and brain zinc levels in rats. Chronic treatment with citalopram (but not with imipramine or ECS) significantly (approx 20%) increased the serum zinc level. Chronic treatment with both drugs slightly (by approx 10%) increase the zinc level in the hippocampus and slightly decreased it in the cortex, cerebellum and basal forebrain. Calculation of the ratio hippocampus/brain region within each group demonstrated a significantly (approx 20%) higher value after treatment with either imipramine or citalopram. Moreover, chronic ECS induced a significant increase (by 30%) in the zinc level in the hippocampus and also a slight increase (by 11–15%) in the other brain regions. Thus, these different antidepressant therapies induced an elevation of the hippocampal zinc concentration, which indicates a significant role of zinc in the mechanism of antidepressant therapy.     

Chronic treatment with zinc and antidepressants induces enhancement of presynaptic/extracellular zinc concentration in the rat prefrontal cortex

Zinc exhibits antidepressant-like activity in preclinical tests/models. Moreover, zinc homeostasis is implicated in the pathophysiology of affective disorders. The aim of the present study was to examine the effect of chronic zinc, citalopram and imipramine intraperitoneal administration on the presynaptic and extracellular zinc concentration in the rat prefrontal cortex and hippocampus. We used two methods: zinc–selenium histochemistry (which images the pool of presynaptic-vesicle zinc) and anodic stripping voltammetry (ASV) for zinc determination in microdialysate (which assays the extracellular zinc concentration). We report that chronic (14×) zinc (hydroaspartate, 10 and 65 mg/kg) and citalopram (20 mg/kg) administration increased the pool of presynaptic zinc (by 34, 50 and 37%, respectively) in the rat prefrontal cortex. The 21% increase induced by imipramine (20 mg/kg) was marginally significant. Likewise, zinc (hydroaspartate, 65 mg/kg), citalopram and imipramine increased the extracellular zinc (although with a different pattern: time point, area under the curve and/or basal level) in this brain region. Furthermore, zinc induced an increase in presynaptic (by 65%) and extracellular zinc (by 90%) in the hippocampus, while both citalopram and imipramine did not. These results indicate that all of the treatments increase presynaptic/extracellular zinc concentrations in the rat prefrontal cortex, which may then contribute to their antidepressant mechanisms. Alterations induced by zinc (but not antidepressants) administration in the hippocampus may be related to specific zinc mechanisms. All the data (previous and present) on the effect of antidepressant treatments on the presynaptic/extracellular zinc concentrations suggest the involvement of this biometal presynaptic/synaptic homeostasis in the antidepressant mechanism(s).     

Species-scanning mutagenesis of the serotonin transporter reveals residues essential in selective, high-affinity recognition of antidepressants

The serotonin transporter (SERT) is a high-affinity sodium/chloride-dependent neurotransmitter transporter responsible for reuptake of serotonin from the extracellular space. SERT is a selective target of several clinically important antidepressants. In a cross-species analysis comparing human and bovine SERTs, the kinetic parameters for serotonin uptake were found to be similar, however, the pharmacological profiles of the two transporters differ. Following transient expression in COS-1 cells, IC(50) values were determined for several antidepressants and psychostimulants. The potencies of the antidepressants citalopram, fluoxetine, paroxetine and imipramine were several-fold higher at hSERT compared with bSERT. No species selectivity was observed for the antidepressants fluvoxamine, and sertraline or for the psychostimulants cocaine, the cocaine analogue beta-carbomethoxy-3beta-(4-iodophenyl)tropane, or for 3,4-methylenedioxymethamphetamine (MDMA). Analysis of six hSERT/bSERT chimeras and subsequent species-scanning mutagenesis of each isoform revealed methionine-180, tyrosine-495, and phenylalanine-513 to be responsible for the increase in citalopram and paroxetine potencies at hSERT and methionine-180 and phenylalanine-513 to confer species selectivity at hSERT for fluoxetine and imipramine. Results were obtained by doing the forward, bovine to human, mutations and confirmed by doing the reverse mutations. Citalopram analogues were used to define the roles of methionine-180, tyrosine-495, and phenylalanine-513 and to reveal molecular interactions with individual functional groups of citalopram. We suggest that methionine-180 interacts with the heterocyclic nucleus of citalopram or stabilizes the binding pocket and phenylalanine-513 to be a steric blocker of antidepressant recognition.     

Inhibition of acetylcholinesterase from Electrophorus electricus (L.) by tricyclic antidepressants

The effects of tricyclic antidepressants drugs (TCA) amitriptyline, imipramine and nortriptyline, on purified Electrophorus electricus (L.) acetylcholinesterase (AChE; acetylcholine hydrolase, EC 3.1.1.7) were studied using kinetic methods and specific fluorescent probe propidium. The antidepressants inhibited AChE activity by a non-competitive mechanism. Inhibition constants range from 200 to 400 microM. Dimethylated amitriptyline and imipramine were more potent inhibitors than the monomethylated nortriptyline. Fluorescence measurements using bis-quaternary ligand propidium were used to monitor ligand-binding properties of these cationic antidepressants to the AChE peripheral anionic site (PAS). This ligand exhibited an eight-fold fluorescence enhancement upon binding to the peripheral anionic site of AChE from E. electricus (L.) with K(D)=7 x 10(-7)M. It was observed that TCA drugs displaced propidium from the enzyme. On the basis of the displacement experiments antidepressant dissociation constants were determined. Similar values for the inhibition constants suggest that these drugs have similar affinity to the peripheral anionic site. The results also indicate that the catalytic active center of AChE does not participate in the interaction of enzyme with tricyclic antidepressants. These studies suggest that the binding site for tricyclic antidepressants is located at the peripheral anionic site of E. electricus (L.) acetylcholinesterase.     

An enhanced sensitivity of muscarinic cholinergic receptor associated with dopaminergic receptor subsensitivity after chronic antidepressant treatment

The chronic effects of antidepressant treatment on striatal dopaminergic (DA) and muscarinic cholinergic (mACh) receptors of the rat brain have been examined comparatively in this study using ³H- spiroperidol (³H-SPD) and ³H-quinuclidinyl benzilate (³H-QNB) as the respective radioactive ligands. Imipramine and desipramine were used as prototype antidepressants. Although a single administration of imipramine or desipramine did not affect each receptor sensitivity, chronic treatment with each drug caused a supersensitivity of mACh receptor subsequent to DA receptor subsensitivity. Furthermore, it has been suggested that anti-mACh properties of imipramine or desipramine may not necessarily be related to the manifestation of mACh receptor supersensitivity and that sustained DA receptor subsensitivity may play some role in the alterations of mACh receptor sensitivity.     

Secretory processing of the Alzheimer amyloid beta/A4 protein precursor is increased by protein phosphorylation.

The 39-43 residue polypeptide (amyloid beta protein, beta A4) deposited as amyloid in Alzheimer's disease (AD) is derived from a set of 695-770 residue precursors referred to as the amyloid beta A4 protein precursor (beta APP). In each of the 695, 751, and 770 residue precursors, the 43 residue beta A4 is an internal peptide that begins 99 residues from the COOH-terminus of the beta APP. Each holoform is normally cleaved within the beta A4 to produce a large secreted derivative as well as a small membrane associated fragment. Neither of these derivatives can produce amyloid because neither contains the entire beta A4 peptide. In this study, we employ cells stably transfected with full length beta APP695, beta APP751, or beta APP770 expression constructs to show that phorbol ester activation of protein kinase C substantially increases the production of secreted forms from each isoform. By increasing processing of beta APP in the secretory pathway, PKC phosphorylation may help to prevent amyloid deposition.     

Increased Secretion of the Amino-Terminal Fragment of Amyloid Precursor Protein in Brains of Rats with a Constitutive Up-Regulation of Protein Kinase C

Abstract: Protein kinase C (PKC) activation stimulates release of secreted amyloid precursor protein (APP_s) in several cell lines. To ascertain the role of PKC in regulating APP metabolism in vivo, we used an animal model (methylazoxymethanol-treated rats; MAM rats) in which PKC is permanently hyperactivated in selected brain areas, i.e., cortex and hippocampus. A significant decrease in membrane-bound APP concentration was found in synaptosomes derived from cortex and hippocampus of MAM rats, where PKC is up-regulated, with a concomitant increase in APP_s production in soluble fractions of the same brain areas. In contrast, in a brain area not affected by MAM treatment (i.e., cerebellum), APP secretion is similar in control and MAM rats, indicating that altered metabolism of APP is restricted to only those areas in which the PKC system is up-regulated. In addition, phorbol esters or H-7 modulate APP_s release in hippocampal slices from both control and MAM rats, further supporting an in vivo role for this enzyme in regulating metabolism of mature APP.     

Acute effects of combining citalopram and pindolol on regional brain serotonin synthesis in sham operated and olfactory bulbectomized rats

The olfactory bulbectomized (OBX) rat is considered to be a good model of the pathology of human depression and also of the functional actions of antidepressant drug therapy. It has been proposed that antidepressant effects of selective serotonin reuptake inhibitors (SSRIs) can be accelerated by blocking 5-HT_1A/B autoreceptors with pindolol. The underlying mechanism is thought to involve acute unrestricting of 5-HT release and, consequently, relatively enhanced 5-HT turnover throughout the forebrain serotonergic networks. The effect of this combination on 5-HT turnover in sham operated or OBX rats can be assessed at the level of 5-HT synthesis, a very important presynaptic step in serotonergic neurotransmission, using the α-[¹⁴C]methyl-l-tryptophan autoradiography method. In sham rats, acute citalopram (20 mg/kg) treatment increased synthesis at almost all serotonergic terminal regions but slightly decreased synthesis at serotonergic cell body regions (i.e. dorsal and median (not significant) raphe; ～16%). Combining pindolol (10 mg/kg) with citalopram further increased synthesis at many regions in sham rats (relative to treatment with only citalopram). In OBX rats, citalopram decreased synthesis at a few terminal regions and greatly decreased synthesis at the dorsal and median raphe (～45%; relative to OBX rats treated with saline). Combining pindolol with citalopram greatly increased synthesis at almost all regions in OBX rats (relative to treatment with only citalopram). These results suggest that acute citalopram effects result in elevated terminal 5-HT synthesis, but these effects are restrained by 5-HT_1A/B autoreceptor feedback to different degrees in sham and OBX rats. Moreover, 5-HT_1A/B autoreceptor feedback is stronger in OBX rats and may underlie the delay of SSRI effects in OBX rats and, correspondingly, in human depression. Pindolol acceleration and augmentation of SSRI antidepressant therapy for human depression may be mediated by attenuation of 5-HT_1A/B autoreceptor feedback, permitting unhindered SSRI effects on serotonergic terminals.     

Distinct Effects of Imipramine on 5-Hydroxytryptamine Uptake Mediated by the Recombinant Rat Serotonin Transporter SERT1

Abstract: Tricyclic and nontricyclic serotonin [5-hydroxytryptamine (5-HT)] uptake inhibitors are widely used for the treatment of depression. Here, we show that both the tricyclic antidepressant imipramine and the nontricyclic antidepressant citalopram competitively inhibit 5-HT transport mediated by the recombinant rat 5-HT transporter SERT1. For citalopram, the concentration producing half-maximal transport inhibition was in the same order of magnitude as its K _D value determined by equilibrium binding. In contrast, the inhibitory potency of imipramine was more than one order of magnitude lower than its K _D value. Our data are consistent with low-affinity imipramine binding occurring at or close to the substrate recognition site, which also binds citalopram. Occupation of the high-affinity imipramine binding site on SERT1 did not affect 5-HT transport but allosterically displaced citalopram from the substrate recognition site. Consequently, low concentrations of imipramine partially protected 5-HT transport from citalopram inhibition. This protection was only observed in the presence of Na⁺ because high-affinity imipramine binding is strictly sodium-dependent. Thus, depending on which of its binding sites on SERT1 is occupied, imipramine may exert distinct effects on 5-HT uptake mediated by the recombinant rat 5-HT transporter.     

Distribution of Specific High-Affinity Binding Sites for [3H]Imipramine in Human Brain

Abstract: [³H]Imipramine binds with high affinity to membranes from different regions of the human brain. The highest density of binding sites was observed in the hypothalamus and substantia nigra and the lowest density in the white matter and cerebellum. As found in rat brain, tricyclic antidepressant drugs are potent inhibitors of [³H]imipramine binding. Atypical antidepressants are, however, much weaker at inhibiting the specific binding. The [³H]imipramine binding site in human cortex is apparently identical to the site already described in the rat brain and in human platelets.     

Antidepressants attenuate the dexamethasone-induced decrease in viability and proliferation of human neuroblastoma SH-SY5Y cells: A involvement of extracellular regulated kinase (ERK1/2)

Excessive glucocorticoid levels in depressed patients have been associated with atrophic changes in some brain regions, but only few studies suggest that some antidepressants can interfere with deleterious effect of glucocorticoids on neuronal cells. The aim of the present study was to examine the effect of dexamethasone (DEX), a synthetic glucocorticoid and some antidepressants from different chemical groups (imipramine, desipramine, amitriptyline, citalopram, fluoxetine, reboxetine and tianeptine) on SH-SY5Y cells cultured in the medium containing steroid-free serum. DEX in concentrations from 1 to 100 μM did not change LDH release but exposure to 10 μM and 100 μM DEX for 24, 48 and 72 h caused a significant reduction in cell viability and proliferation as confirmed by MTT reduction and BrdU ELISA assays, respectively. Twenty four-hour incubation of cells with antidepressants (0.05–10 μM) and DEX (10 μM) showed that imipramine, amitriptyline, desipramine, citalopram and fluoxetine at concentrations from 0.1 up to 1 μM, reboxetine (0.1 μM) and tianeptine (0.05 μM) prevented the DEX-induced decreases in cell viability and proliferation rate. The protective effects of antidepressants were ameliorated by inhibitors of MAPK/ERK1/2, but not PI3-K/Akt pathway as shown for imipramine, fluoxetine and reboxetine. Moreover, Western blot analysis showed the decrease in the activated form of ERK1/2 (p-ERK) after DEX treatment and this effect was inhibited by imipramine. Thus, the reduction in SH-SY5Y cell viability caused by DEX appears to be related to its antiproliferative activity and some antidepressant drugs in low concentrations attenuate this effect by mechanism which involves the activation of MAPK/ERK1/2 pathway.     

Alzheimer's disease and control brain contain soluble derivatives of the amyloid protein precursor that end within the beta amyloid protein region.

The 39-43 amino acid beta amyloid protein (A beta) that deposits as amyloid in the brains of patients with Alzheimer's disease (AD) is encoded as an internal sequence within a larger membrane-associated protein known as the amyloid protein precursor (APP). In cultured cells, the APP is normally cleaved within the A beta to generate a large secreted derivative and a small membrane-associated fragment. Neither of these derivatives can produce amyloid because neither contains the entire A beta. Our study was designed to determine whether the soluble APP derivatives in human brain end within the A beta as described in cell culture or whether AD brain produces potentially amyloidogenic soluble derivatives that contain the entire A beta. We find that both AD and control brain contain nonamyloidogenic soluble derivatives that end at position 15 of the A beta. We have been unable to detect any soluble derivatives that contain the entire A beta in either the AD or control brain.     

Alterations in serum and brain trace element levels after antidepressant treatment. Part II. Copper

We have studied the effect of chronic treatment with imipramine, citalopram, and electroconvulsive shock (ECS) on serum and brain copper levels in rats. Chronic treatment with citalopram and imipramine (but not ECS) significantly (approx 14%) decreased the serum copper level. Chronic treatment with both drugs did not alter the brain copper level. However, chronic ECS induced a significant increase (by 36%) in the copper level in the hippocampus and also in the cerebellum (by 16%). In contrast to the zinc, where both pharmacologic and ECS treatment increased its hippocampal concentration, these two antidepressant therapy (drugs versus ECS) differ in their effect on brain copper level. These findings suggest that the mechanism by which copper is involved in ECS differs from that of any involvement in the action of the drugs studied.     

Imipramine stimulates phospholipase C activity in rat brain

We previously demonstrated that antidepressant drugs (ADs) cause Ca²⁺ release from inositol 1,4,5-trisphosphate-sensitive Ca²⁺ stores in cultured neurons of rat frontal cortex. The present study examines the mechanism by which tricyclic ADs activate phospholipase C (PLC) in rat frontal cortex. Using an exogenous substrate to measure PLC activity, we demonstrated that a tricyclic AD, imipramine, stimulated PLC activity of the frontal cortex membrane in a concentration-dependent manner. Two tricyclic ADs, desipramine and amitriptyline, also stimulated PLC activity, while Li⁺ or pargyline had no effect on PLC activity. Although imipramine did not activate PLC in the membrane in the absence of Ca²⁺, imipramine synergistically activated PLC in the presence of Ca²⁺. This result indicates that the mechanism of PLC activation by imipramine is different from its activation by Ca²⁺. Imipramine stimulated PLC activity in the cytosol of rat frontal cortex as well as in the membrane. Preincubation of the cytosol with anti-PLC-β₁ antibody prevented the imipramine-mediated activation of PLC. However, preincubation with anti-PLC-γ₁ or anti-PLC-δ₁ did not prevent activation of PLC. These results suggest that imipramine activates PLC-β₁ directly without receptor or guanine nucleotide binding protein mediation.     

BRI2 protein regulates β-amyloid degradation by increasing levels of secreted insulin-degrading enzyme (IDE)

The amyloid precursor protein (APP) is one of the major proteins involved in Alzheimer disease (AD). Proteolytic cleavage of APP gives rise to amyloid-β (Aβ) peptides that aggregate and deposit extensively in the brain of AD patients. Although the increase in levels of aberrantly folded Aβ peptide is considered to be important to disease pathogenesis, the regulation of APP processing and Aβ metabolism is not fully understood. Recently, the British precursor protein (BRI2, ITM2B) has been implicated in influencing APP processing in cells and Aβ deposition in vivo. Here, we show that the wild type BRI2 protein reduces plaque load in an AD mouse model, similar to its disease-associated mutant form, ADan precursor protein (ADanPP), and analyze in more detail the mechanism of how BRI2 and ADanPP influence APP processing and Aβ metabolism. We find that overexpression of either BRI2 or ADanPP reduces extracellular Aβ by increasing levels of secreted insulin-degrading enzyme (IDE), a major Aβ-degrading protease. This effect is also observed with BRI2 lacking its C-terminal 23-amino acid peptide sequence. Our results suggest that BRI2 might act as a receptor protein that regulates IDE levels that in turn influences APP metabolism in a previously unrecognized way. Targeting the regulation of IDE may be a promising therapeutic approach to sporadic AD.     

Synthesis and antidepressant-like activity evaluation of sulphonamides and sulphonyl-hydrazones

In this study a series of sulphonamides and sulphonyl hydrazones of maleimide, naphthalimide and phthalimide derivatives was synthesized. The antidepressant effect of these compounds was evaluated by the forced-swimming test in mice. The behavioural parameter observed in this test is a reduction in the immobility time, which is indicative of antidepressant activity. All compounds, except 8, 11 and 24, were active as antidepressants. The most active compound was the sulphonyl-hydrazone 10 which showed an activity of around 72.02% at 60 mg/kg, it thus being more active than imipramine (10mg/kg, ip), a commercial antidepressant. Other important results were obtained for the benzylnaphthalimide derivatives, the sulphonamides 21 and 22 showing activity of 64% at 10mg/kg, also being more active than imipramine. These results indicate that the sulphonamides and sulphonyl-hydrazone cyclic imide derivatives are potential compounds for use in the designing of new candidates for the treatment of depression.