Effects of trifluoperazine, a calmodulin antagonist, on rabbit T- and B-cell responses to mitogens and antigen

The genetics of vascular incidents associated with second-generation antipsychotic administration

Second-generation antipsychotics (SGA) have been associated with risk of stroke in elderly patients, but the molecular and genetic background under this association has been poorly investigated. The aim of the present study was to prioritize a list of genes with an SGA altered expression in order to characterize the genetic background of the SGA-associated stroke risk. Genes with evidence of an altered expression after SGA treatments in genome-wide investigations, both in animals and men, were identified. The Genetic Association Database (GAD) served to verify which of these genes had a proven positive association with an increased stroke risk, and along with it each evidence was tested and recorded. Seven hundred and forty five genes had evidence of a change of their expression profile after SGA administration in various studies. Nine out of them have also been significantly related to an increased strokes risk. We identified and described nine genes as potential candidates for future genetic studies aimed at identifying the genetic background of the SGA-related stroke risk. Further, we identify the molecular pathways in which these genes operate in order to provide a molecular framework to understand on which basis SGA may enhance the risk for stroke.

Inhibition of human ether-a-go-go-related gene K+ channel and IKr of guinea pig cardiomyocytes by antipsychotic drug trifluoperazine

Trifluoperazine, a commonly used antipsychotic drug, has been known to induce QT prolongation and torsades de pointes, which can cause sudden death. We studied the effects of trifluoperazine on the human ether-a-go-go-related gene (HERG) channel expressed in Xenopus oocytes and on the delayed rectifier K(+) current of guinea pig cardiomyocytes. The application of trifluoperazine showed a dose-dependent decrease in current amplitudes at the end of voltage steps and tail currents of HERG. The IC(50) for a trifluoperazine block of HERG current progressively decreased according to depolarization: IC(50) values at -40, 0, and +40 mV were 21.6, 16.6, and 9.29 microM, respectively. The voltage dependence of the block could be fitted with a monoexponential function, and the fractional electrical distance was estimated to be delta = 0.65. The block of HERG by trifluoperazine was use-dependent, exhibiting more rapid onset and greater steady-state block at higher frequencies of activation; there was partial relief of the block with decreasing frequency. In guinea pig ventricular myocytes, bath applications of 0.5 and 2 microM trifluoperazine at 36 degrees C blocked the rapidly activating delayed rectifier K(+) current by 32.4 and 72.9%, respectively; however, the same concentrations of trifluoperazine failed to significantly block the slowly activating delayed rectifier K(+) current. Our findings suggest the arrhythmogenic side effect of trifluoperazine is caused by a blockade of HERG and the rapid component of the delayed rectifier K(+) current rather than by the blockade of the slow component.

The voltage- and time-dependent blocking effect of trifluoperazine on T lymphocyte Kv1.3 channels

Phenothiazines are well-known calmodulin inhibitors that interact with many receptors and channels including a variety of potassium channels. In this study, we report a blocking effect of trifluoperazine (TFP) on voltage-gated Kv1.3 channels expressed in human T lymphocytes. Application of TFP in the concentration range from 1 to 20 microM reduced the current amplitude to about a half of the control value. The currents were blocked to less than 0.05 of the control value at 50 microM TFP concentration. The blocking effect was accompanied by a substantial increase in the current inactivation rate, whereas the activation rate and the steady-state activation and inactivation were not changed significantly. The blocking effect of TFP was voltage dependent being most potent at +60mV and least potent at -20mV. The blocking effect of TFP on the currents and the recovery from block was time dependent. Other calmodulin antagonists: tamoxifen (TMX) and thioridazine also inhibited the channels at micromolar concentrations. The effects exerted by TMX and thioridazine resembled the inhibitory effect of TFP. The blocking effect of thioridazine was time dependent and appeared to be more potent that the inhibition by TFP and TMX. TFP, TMX and thioridazine inhibited the activity of Kv1.3 channels only when applied extracellularly. The inhibitory effect of all the compounds was reversible. The possible physiological significance of the current inhibition is discussed.

Suppression of natural killer cell activity in mouse spleen lymphocytes by several dopamine receptor antagonists

The effects of dopaminergic receptor inhibitors such as thiothixine (D1/D2), fluphenazine (D1/D2), trifluoperazine (D1/D2), pimozide (D2), flupenthixol (D1/D2), (+/-)-SKF 83566 (D1), and spiperone (D2) on splenic natural killer (NK) cell cytotoxic activities were assessed in vitro using mouse spleen lymphocytes or enriched NK cells. Both the activities of the splenic NK cell cytotoxicity and the effector-target cell conjugation were suppressed by thiothixine, fluphenazine, and trifluoperazine at concentrations from 2.64 to 14.78 microM. In addition, the augmentation of the cytolytic activity of NK cells induced by interferon-alpha or interleukin-2 was antagonized by pretreatment with these neuroleptic compounds. However, neither the splenic NK cell cytotoxicity nor the effector-target cell conjugation were affected by treatment with other neuroleptic compounds such as pimozide, flupenthixol, (+/-)-SKF 83566, and spiperone. Thus, it appears that neuroleptic compounds such as thiothixine, fluphenazine, and trifluoperazine may act through the mechanisms other than a dopaminergic pathway to affect the NK cell-target cell interaction.

Identification of a calmodulin-binding and inhibitory peptide domain in the HIV-1 transmembrane glycoprotein

A number of studies suggest a critical role of the HIV-1 envelope glycoprotein in cytopathogenesis, but the detailed mechanisms of cell injury remain to be defined. HIV-1 envelope proteins associate with the host cell membrane, and studies have demonstrated that HIV perturbs membrane structure and function. We describe here a structurally conserved region of the HIV-1 transmembrane protein (TM) that displays functional properties of target regions of proteins that interact directly with calcium-saturated calmodulin as part of cellular response cascades. The synthetic peptide homolog encompassing the carboxyl terminus (amino acid residues 828-855) of HIV-1 TM protein (LLP-1) is shown in standard in vitro assays to bind efficiently to purified calmodulin (CaM) and to inhibit in vitro CaM-mediated stimulation of phosphodiesterase activity. This suggests that this peptide homolog binds to CaM at affinities similar to those reported for a reference CaM-binding peptide. In addition, the CaM-dependent process of phospholipid synthesis can be inhibited in cell cultures by exogenous addition of the LLP-1. Finally, we have shown that the full-length TM protein binds CaM, whereas a truncated TM protein lacking the LLP-1 segment does not bind CaM. These results suggest a novel mechanism of viral cytopathogenesis mediated by the interaction of HIV-1 TM protein with cellular CaM, that could lead to an uncoupling of critical cellular signal transduction pathways.

Dissociation of immunosuppression by chlorpromazine and trifluoperazine from pharmacologic activities as dopamine antagonists

Neuroleptic compounds may affect the immune system through a variety of mechanisms. Most possess a complex pharmacology, which makes specific, causal relationships difficult to discern. In this study, a series of experiments was performed to examine the effects of dopamine antagonists on a battery of immunologic parameters. Mitogen-induced lymphocyte proliferation in vitro was inhibited by haloperidol, chlorpromazine, and trifluoperazine at 10, 1 and 1 microM concentrations, respectively. Sulpiride and metoclopramide had no direct effect in vitro. In vivo lymphocyte proliferation was significantly reduced by chlorpromazine at the highest tested doses (12.5 and 15 mg/kg) and by trifluoperazine at the highest tested dose (30 mg/kg). All other dopamine antagonists had no significant effect on in vivo lymphocyte proliferation. A murine graft vs host (GVH) response was unaffected by haloperidol, sulpiride, and metoclopramide. Chlorpromazine and trifluoperazine exhibited significant inhibition of the GVH response at the highest doses only (15 and 30 mg/kg, respectively). In a picryl chloride induced delayed type hypersensitivity (DTH) assay, haloperidol, metoclopramide, and sulpiride had no effect. However, both chlorpromazine and trifluoperazine significantly reduced DTH-induced paw swelling at the higher doses (7.5 mg/kg, and 10 and 30 micrograms/kg, respectively). These studies indicate that the more specific dopamine antagonists (e.g. sulpiride, metoclopramide, and haloperidol) do not share the immunologic profiles of chlorpromazine and trifluoperazine, suggesting that these effects of chlorpromazine and trifluoperazine are not related to their dopamine antagonist properties.

The effect of calcium channel blockers and calmodulin inhibitors on the macrophage factor-stimulated synthesis of collagenase by rabbit chondrocytes

Macrophages and monocytes secrete a factor(s) which can stimulate the synthesis of collagenase in synovial cells and in chondrocytes. Incubation of rabbit chondrocytes with macrophage conditioned medium (MCM) and with the calcium channel blockers, nifedipine, verapamil or diltiazem (up to 200 microM) had no effect on collagenase synthesis. However, TMB-8 (8-[N,N-diethylamino]-octyl 3,4,5-trimethoxybenzoate hydrochloride), an inhibitor of internal calcium movement, did inhibit the process with an IC50 of approximately 130 microM. The calmodulin antagonists, trifluoperazine, chlorpromazine and calmidazolium (R-24571) were effective inhibitors of the process with IC50's of 40 microM, 18 microM and 3.5 microM, respectively. Collagenase activity itself was not affected by these agents. The data suggests that calmodulin and/or internal calcium movement may play a role in the macrophage factor-stimulated synthesis of collagenase in rabbit chondrocytes.

Early steps in interferon-gamma production: possible involvement of Ca2+-calmodulin-dependent enzymes

A23187 in combination with phorbol myristate acetate (PMA) strongly induces production of interferon-gamma (IFN-gamma) by human peripheral blood mononuclear cells (PBMC) and even by murine PBMC, which respond poorly to A23187 alone. Macrophage depletion of PBMC strongly reduces IFN-gamma production induced by several mitogens, but does not affect IFN-gamma production induced by A23187 and PMA. In addition the same stimuli are able in combination to induce strong amounts of IFN-gamma, even in the Jurkat T cell line. The protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H-7) and the calmodulin antagonist N-(6-aminoehexyl)-5-chloro-1-naphthalenesulfonamide (W-7) were examined for their ability to inhibit IFN-gamma production induced by PMA and A23187. At concentrations near the Ki for protein kinase C, H-7 failed to inhibit PMA- and A23187-induced IFN-gamma production. In contrast, W-7 at low concentrations inhibited IFN-gamma production induced by the same stimuli. In addition OAG, which is known to directly activate protein kinase C, failed to act synergistically with A23187 in the induction of IFN-gamma. On the basis of these results we propose that A23187 and PMA may mimic the early steps of lymphocyte activation, without the requirement of macrophage, bypassing antigen-, or lectin-induced signal. Our results suggest that Ca2+-calmodulin-dependent reactions other than protein kinase C activation may be essential for IFN-gamma production, at least at level of the producing cells.

Molecular signaling mechanisms in T-lymphocyte activation pathways: a review and future prospects

Understanding of the molecular mechanisms which drive the complex activation responses of T lymphocytes was previously limited. However, current studies in lymphocytes, and in other cells, have indicated the involvement of several secondary messenger or signal systems, and recent progress in elucidating the relevant pathways has been extraordinarily rapid. This review therefore attempts to provide an overview of these processes--including the effects of Ca2+, hydrolysis of phospholipids, arachidonic acid, Ca2+/phospholipid-dependent and tyrosine kinases, calmodulin, cyclic nucleotides, ion channels, and adherent cells--and their roles in weaving a subtle and highly responsive web of regulatory signals.

Calmodulin in lymphocyte mitogenic stimulation and in lymphoid cell line growth

Calmodulin levels are elevated three- to fourfold in the dividing cells, resulting from the lectin-induced stimulation of fresh human lymphocytes. This increase in calmodulin appears to be related mainly to progression into S phase and supports the hypothesis that calmodulin might be crucial in regulating the progression of lymphoblasts through their division cycle. Calmodulin levels are higher in a lymphoid cell line derived from human acute lymphoblastic leukemia blood cells than in a lymphoid cell line derived from normal human blood cells, suggesting that calmodulin could be an important mediator of the leukemogenetic process.

Nifedipine-induced hyporeactivity in delayed hypersensitivity skin tests

Four patients and three healthy volunteers were submitted to delayed hypersensitivity skin tests to candidin, tuberculin, streptokinase/streptodornase (SK/SD) and mumps antigen before and after a 1 week treatment with nifedipine 10 mg q. 8h. A decrease in the scores of induration and erythema was observed, especially in response to SK/SD antigen challenge. We conclude that nifedipine may induce an anergy status in delayed hypersensitivity skin tests.

Does the binding of cyclosporine to calmodulin result in immunosuppression?

The cyclosporines are a family of cyclic endecapeptides that cause a profound suppression of primary immune stimulation both in vitro and in vivo. Recently, the regulatory protein calmodulin (CaM) has been implicated as a target for cyclosporin A (CsA) binding. This study utilized two less-active isomers of CsA to evaluate the specificity and biological significance of CaM binding. The three cyclosporines exhibited equivalent in vitro binding to CaM, regardless of immunosuppressive activity. Furthermore, CaM-dependent enzyme systems were inhibited equally by active and inactive cyclosporines, but only at concentrations 100 times those necessary to block lymphocyte activation. Thus the exquisite immunosuppressive stereospecificity displayed by cyclosporine isomers is not reflected in the binding to and inhibition of CaM, suggesting that inhibition of CaM-dependent processes is not sufficient to explain the immunosuppressive activity of CsA.

Inhibition of T3 mediated T-cell proliferation by Ca2+-channel blockers and inhibitors of Ca2+/phospholipid-dependent kinase

The potential roles of Ca2+ ions in the response of T lymphocytes to stimulation with monoclonal antisera to the T3 antigen were investigated by means of pharmacological agents that predominantly inhibit the flux of Ca2+ ions into cells (verapamil, nifedipine) or the activity of Ca2+-dependent kinases (trifluoperazine, polymyxin B). As assessed by uptake of [3H]thymidine, proliferation induced with anti-T3 +/- recombinant IL-2 at 72 h was inhibited by greater than 80% in the presence of nifedipine at 50 microM, and almost completely arrested (greater than 95% inhibition) with the other agents at the same concentration. Further quantitative assays of the effects of polymyxin B and trifluoperazine on C-kinase labelling of exogenous substrate showed a major reduction with both agents, but inhibition was substantially greater with polymyxin B that with trifluoperazine (IC50 = 14 and 70 microM respectively). These results were confirmed by qualitative assessment of Ca2+/phospholipid-dependent phosphorylation of endogenous substrates, which demonstrated major phosphoproteins of MW 56,000, 52,000, 43,000, and 20,000, and dose-dependent reduction in labelling in the presence of polymyxin B. Similar results were obtained under more physiological conditions in intact cells labelled with 32P orthophosphate. These findings indicate several possible roles for Ca2+ in T-cell activation, and several possible levels of activity, including modulation of calmodulin-dependent kinases and effects on Ca2+/phospholipid-dependent kinases and Ca2+ channels.