Modifications of phospholipid metabolism induced by chlorpromazine, desmethylimipramine and propranolol in C6 glioma cells

ARL-17477 is a dual inhibitor of NOS1 and the autophagic-lysosomal system that prevents tumor growth in vitro and in vivo

ARL-17477 is a selective neuronal nitric oxide synthase (NOS1) inhibitor that has been used in many preclinical studies since its initial discovery in the 1990s. In the present study, we demonstrate that ARL-17477 exhibits a NOS1-independent pharmacological activity that involves inhibition of the autophagy-lysosomal system and prevents cancer growth in vitro and in vivo. Initially, we screened a chemical compound library for potential anticancer agents, and identified ARL-17477 with micromolar anticancer activity against a wide spectrum of cancers, preferentially affecting cancer stem-like cells and KRAS-mutant cancer cells. Interestingly, ARL-17477 also affected NOS1-knockout cells, suggesting the existence of a NOS1-independent anticancer mechanism. Analysis of cell signals and death markers revealed that LC3B-II, p62, and GABARAP-II protein levels were significantly increased by ARL-17477. Furthermore, ARL-17477 had a chemical structure similar to that of chloroquine, suggesting the inhibition of autophagic flux at the level of lysosomal fusion as an underlying anticancer mechanism. Consistently, ARL-17477 induced lysosomal membrane permeabilization, impaired protein aggregate clearance, and activated transcription factor EB and lysosomal biogenesis. Furthermore, in vivo ARL-17477 inhibited the tumor growth of KRAS-mutant cancer. Thus, ARL-17477 is a dual inhibitor of NOS1 and the autophagy-lysosomal system that could potentially be used as a cancer therapeutic.

Treatment of cancer with antipsychotic medications: Pushing the boundaries of schizophrenia and cancer

Over a century ago, the phenothiazine dye, methylene blue, was discovered to have both antipsychotic and anti-cancer effects. In the 20th-century, the first phenothiazine antipsychotic, chlorpromazine, was found to inhibit cancer. During the years of elucidating the pharmacology of the phenothiazines, reserpine, an antipsychotic with a long historical background, was likewise discovered to have anti-cancer properties. Research on the effects of antipsychotics on cancer continued slowly until the 21st century when efforts to repurpose antipsychotics for cancer treatment accelerated. This review examines the history of these developments, and identifies which antipsychotics might treat cancer, and which cancers might be treated by antipsychotics. The review also describes the molecular mechanisms through which antipsychotics may inhibit cancer. Although the overlap of molecular pathways between schizophrenia and cancer have been known or suspected for many years, no comprehensive review of the subject has appeared in the psychiatric literature to assess the significance of these similarities. This review fills that gap and discusses what, if any, significance the similarities have regarding the etiology of schizophrenia.

Mass spectrometry imaging reveals lipid upregulation and bile acid changes indicating amitriptyline induced steatosis in a rat model

As a consequence of the detoxification process, drugs and drug related metabolites can accumulate in the liver, resulting in drug induced liver injury (DILI), which is the major cause for dose limitation. Amitriptyline, a commonly used tricyclic anti-depressant, is known to cause DILI. The mechanism of Amitriptyline induced liver injury is not yet completely understood. However, as it undergoes extensive hepatic metabolism, unraveling the molecular changes in the liver upon Amitriptyline treatment can help understand Amitriptyline's mode of toxicity. In this study, Amitriptyline treated male rat liver tissue was analyzed using Matrix Assisted Laser Desorption/Ionization-Mass Spectrometry Imaging (MALDI-MSI) to investigate the spatial abundances of Amitriptyline, lipids, and bile acids. The metabolism of Amitriptyline in liver tissue was successfully demonstrated, as the spatial distribution of Amitriptyline and its metabolites localize throughout treatment group liver samples. Several lipids appear upregulated, from which nine were identified as distinct phosphatidylcholine (PC) species. The detected bile acids were found to be lower in Amitriptyline treatment group. The combined results from histological findings, Oil Red O staining, and lipid zonation by MSI revealed lipid upregulation in the periportal area indicating drug induced macrovesicular steatosis (DIS).

Understanding and improving assays for cytotoxicity of nanoparticles: what really matters?

Despite years of excellent individual studies, the impact of nanoparticle (NP) cytotoxicity studies remains limited by inconsistent data collection and analysis. It is often unclear how exposure conditions can be used to determine cytotoxicity quantitatively. Discrepancies due to using different measurement conditions, readouts and controls to characterize NP interactions with cells lead to further challenges. To examine which parameters are critical in NP cytotoxicity studies, we have chosen to examine two NP types (liposomes and quantum dots) at different concentrations incubated with two primary vascular endothelial cells, HUVEC and HMVEC-C for a standard time of 24 h. We paid close attention to the effects of positive controls and cell association on interpretation of cytotoxicity data. Various cellular responses (ATP content, oxidative stress, mitochondrial toxicity, and phospholipidosis) were measured in parallel. Interestingly, cell association data varied significantly with the different image analyses. However, cytotoxicity responses could all be correlated with exposure concentration. Cell type did have an effect on cytotoxicity reports. Most significantly, NP cytotoxicity results varied with the inclusion or exclusion of positive controls. In the absence of positive controls, one tends to emphasize small changes in cell responses to NPs.

Alterations in endo-lysosomal function induce similar hepatic lipid profiles in rodent models of drug-induced phospholipidosis and Sandhoff disease

Drug-induced phospholipidosis (DIPL) is characterized by an increase in the phospholipid content of the cell and the accumulation of drugs and lipids inside the lysosomes of affected tissues, including in the liver. Although of uncertain pathological significance for patients, the condition remains a major impediment for the clinical development of new drugs. Human Sandhoff disease (SD) is caused by inherited defects of the β subunit of lysosomal β-hexosaminidases (Hex) A and B, leading to a large array of symptoms, including neurodegeneration and ultimately death by the age of 4 in its most common form. The substrates of Hex A and B, gangliosides GM2 and GA2, accumulate inside the lysosomes of the CNS and in peripheral organs. Given that both DIPL and SD are associated with lysosomes and lipid metabolism in general, we measured the hepatic lipid profiles in rodent models of these two conditions using untargeted LC/MS to examine potential commonalities. Both model systems shared a number of perturbed lipid pathways, notably those involving metabolism of cholesteryl esters, lysophosphatidylcholines, bis(monoacylglycero)phosphates, and ceramides. We report here profound alterations in lipid metabolism in the SD liver. In addition, DIPL induced a wide range of lipid changes not previously observed in the liver, highlighting similarities with those detected in the model of SD and raising concerns that these lipid changes may be associated with underlying pathology associated with lysosomal storage disorders.

Mechanistic review of drug-induced steatohepatitis

Drug-induced steatohepatitis is a rare form of liver injury known to be caused by only a handful of compounds. These compounds stimulate the development of steatohepatitis through their toxicity to hepatocyte mitochondria; inhibition of beta-oxidation, mitochondrial respiration, and/or oxidative phosphorylation. Other mechanisms discussed include the disruption of phospholipid metabolism in lysosomes, prevention of lipid egress from hepatocytes, targeting mitochondrial DNA and topoisomerase, decreasing intestinal barrier function, activation of the adenosine pathway, increasing fatty acid synthesis, and sequestration of coenzyme A. It has been found that the majority of compounds that induce steatohepatitis have cationic amphiphilic structures; a lipophilic ring structure with a side chain containing a cationic secondary or tertiary amine. Within the last decade, the ability of many chemotherapeutics to cause steatohepatitis has become more evident coining the term chemotherapy-associated steatohepatitis (CASH). The mechanisms behind drug-induced steatohepatitis are discussed with a focus on cationic amphiphilic drugs and chemotherapeutic agents.

Identification of drugs inducing phospholipidosis by novel in vitro data

Drug-induced phospholipidosis (PLD) is a lysosomal storage disorder characterized by the accumulation of phospholipids within the lysosome. This adverse drug effect can occur in various tissues and is suspected to impact cellular viability. Therefore, it is important to test chemical compounds for their potential to induce PLD during the drug design process. PLD has been reported to be a side effect of many commonly used drugs, especially those with cationic amphiphilic properties. To predict drug-induced PLD in silico, we established a high-throughput cell-culture-based method to quantitatively determine the induction of PLD by chemical compounds. Using this assay, we tested 297 drug-like compounds at two different concentrations (2.5 μM and 5.0 μM). We were able to identify 28 previously unknown PLD-inducing agents. Furthermore, our experimental results enabled the development of a binary classification model to predict PLD-inducing agents based on their molecular properties. This random forest prediction system yields a bootstrapped validated accuracy of 86 %. PLD-inducing agents overlap with those that target similar biological processes; a high degree of concordance with PLD-inducing agents was identified for cationic amphiphilic compounds, small molecules that inhibit acid sphingomyelinase, compounds that cross the blood-brain barrier, and compounds that violate Lipinski's rule of five. Furthermore, we were able to show that PLD-inducing compounds applied in combination additively induce PLD.

The antidepressant sertraline targets intracellular vesiculogenic membranes in yeast

Numerous studies have shown that the clinical antidepressant sertraline (Zoloft) is biologically active in model systems, including fungi, which do not express its putative protein target, the serotonin/5-HT transporter, thus demonstrating the existence of one or more secondary targets. Here we show that in the absence of its putative protein target, sertraline targets phospholipid membranes that comprise the acidic organelles of the intracellular vesicle transport system by a mechanism consistent with the bilayer couple hypothesis. On the basis of a combination of drug-resistance selection and chemical-genomic screening, we hypothesize that loss of vacuolar ATPase activity reduces uptake of sertraline into cells, whereas dysregulation of clathrin function reduces the affinity of membranes for sertraline. Remarkably, sublethal doses of sertraline stimulate growth of mutants with impaired clathrin function. Ultrastructural studies of sertraline-treated cells revealed a phenotype that resembles phospholipidosis induced by cationic amphiphilic drugs in mammalian cells. Using reconstituted enzyme assays, we also demonstrated that sertraline inhibits phospholipase A(1) and phospholipase D, exhibits mixed effects on phospholipase C, and activates phospholipase A(2). Overall, our study identifies two evolutionarily conserved membrane--active processes-vacuolar acidification and clathrin-coat formation--as modulators of sertraline's action at membranes.

Screening for the drug-phospholipid interaction: correlation to phospholipidosis

Phospholipid bilayers represent a complex, anisotropic environment fundamentally different from bulk oil or octanol, for instance. Even "simple" drug association to phospholipid bilayers can only be fully understood if the slab-of-hydrocarbon approach is abandoned and the complex, anisotropic properties of lipid bilayers reflecting the chemical structures and organization of the constituent phospholipids are considered. The interactions of drugs with phospholipids are important in various processes, such as drug absorption, tissue distribution, and subcellular distribution. In addition, drug-lipid interactions may lead to changes in lipid-dependent protein activities, and further, to functional and morphological changes in cells, a prominent example being the phospholipidosis (PLD) induced by cationic amphiphilic drugs. Herein we briefly review drug-lipid interactions in general and the significance of these interactions in PLD in particular. We also focus on a potential causal connection between drug-induced PLD and steatohepatitis, which is induced by some cationic amphiphilic drugs.

Drug-induced phospholipidosis: issues and future directions

Numerous drugs containing a cationic amphiphilic structure are capable of inducing phospholipidosis in cells under conditions of in vivo administration or ex vivo incubation. The principal characteristics of this condition include the reversible accumulation of polar phospholipids in association with the development of unicentric or multicentric lamellated bodies within cells. There is an abundance of data providing an understanding of potential mechanisms for the induction of phospholipidosis; however, the process is likely to be complex and may differ from one drug to another. The functional consequences of the presence of this condition on cellular or tissue function are not well understood. The general consensus is that the condition is an adaptive response rather than a toxicological manifestation; however, additional studies to examine this question are needed. Until this issue is resolved, concerns about phospholipidosis will continue to exist at regulatory agencies. Procedures for the screening of potential phospholipogenic candidate compounds are available. In contrast, a clear need exists for the identification of valid biomarkers to assess the development of phospholipidosis in preclinical and clinical studies.

Antidepressant-induced lipidosis with special reference to tricyclic compounds

Cationic amphiphilic drugs, in general, induce phospholipid disturbances. Tricyclic, as well as other antidepressants belong to this group. In experimental animals, antidepressants induce lipid storage disorders in cells of most organs, a so-called generalized phospholipidosis. This disorder is conveniently detected by electron microscopic examination revealing myelin figures. Myelin figures or myeloid bodies are subcellular organelles containing unicentric lamellar layers. The lipidotic induction potency during in vivo is related to the apolarity of the compound. Metabolism of phospholipids takes place within the cell continuously. Several underlying mechanisms may be responsible for the induction of the phospholipid disturbance. For instance, it has been suggested that the compounds bind to phospholipids and such binding may alter the phospholipid's suitability as a substrate for phospholipases. Free TCA or metabolites thereof may also inhibit phospholipases directly, as has been demonstrated for sphingomyelinase in glioma and neuroblastoma cells. Both these mechanisms might result in phospholipidosis. Interaction between drug and phospholipid bilayer has been investigated by nuclear magnetic resonance technique. There seems to be large differences in the sensitivities amongst different organs. Steroid-producing cells of the adrenal cortex, testis and ovaries are in particular susceptible to drug-induced lipidosis. The so-called foam cells are lung macrophages located in the interstitium which become densely packed with myelin figures during TCA exposure. It requires about 3-6 weeks of treatment to develop this converted cell. In cell cultures however, phospholipidosis is demonstrated already after 24 h only. It appears that the cells that undergo TCA-induced lipidosis may recover after withdrawal of the drug. The time required to achieve complete recovery ranges from 3-4 weeks to several months, depending on the organ affected. Little is known about the functional significance of lipidosis. Even if TCA and other antidepressants show other effects, it has not been possible to exclusively relate it to phospholipidosis. However, few attempts have been made to correlate the physiological effects of TCAs in experimental animals to the morphological changes associated with phospholipidosis. There is an increasing evidence however, that cationic amphiphilic drugs may have effects on immune function, signal transduction and receptor-mediated events, effects that to some extent might be related to disturbances in phospholipid metabolism.

Cationic amphiphilic drug-induced phospholipidosis

Phospholipidosis, a phospholipid storage disorder, defines an excessive accumulation of intracellular phospholipids. Phospholipids are structural components of mammalian cytoskeleton and cell membranes. The metabolism of this essential cell component is regulated by the individual cell and may be altered by drugs that interact with phospholipids or the enzymes that affect their metabolism. Xenobiotics or their metabolites that induce phospholipidosis include a wide variety of pharmacologic agents, including antibacterials, antipsychotics, antidepressants, antiarrhythmics, antianginals, antimalarials, anorexic agents, cholesterol-lowering agents, and others. Each of these drugs shares several common physiochemical properties: hydrophobic ring structure on the molecule and a hydrophilic side chain with a charged cationic amine group, hence the class term cationic amphiphilic drugs (CADs). This paper reviews the phospholipid metabolism, physiochemical characteristics of CADs, specificity of phospholipidosis in animals and humans, functional effects of phospholipidosis, interaction of CADs with biologic membranes and lysosome metabolism, influence of CADs on phospholipases and phospholipid synthesis, and a proposed mechanism for induction of phospholipidosis in the lung. In human risk assessment, investigators should consider the many factors in evaluating a drug that induces phospholipidosis in animals. These include: the therapeutic class of drug, presence of active metabolites, tissue or organ selectivity in animals and humans, influence of concurrently administered drugs, reversibility of effect, and other factors that increase or decrease the induction of phospholipidosis. Generalities regarding the etiology, incidence, and effect of the drug on a specific host may not be made. Each drug must be evaluated separately to identify the risk when administered for therapeutic effect in humans.

Chronic treatment with antidepressants, verapamil, or lithium inhibits the serotonin-induced intracellular calcium response in individual C6 rat glioma cells

The effects of chronic treatment with antidepressants, verapamil, or lithium on serotonin (5-HT)-induced Ca2+ increase were investigated in single C6BU-1 glioma cells with digital imaging microscopy. Clomipramine and citalopram, at a concentration of 100 nM, decreased the peak values of 5-HT-induced [Ca2+]i changes. Verapamil (100 nM), a calcium antagonist, and lithium (1 mM) also inhibited the peak amplitudes in the same way. The present findings suggest that chronic treatment with antidepressants, verapamil, or lithium, at therapeutic concentrations, have the common action of inhibiting 5-HT-mediated [Ca2+]i increase.

Essential fatty acid deficiency in erythrocyte membranes from chronic schizophrenic patients, and the clinical effects of dietary supplementation

There is now convincing evidence that membrane phospholipid metabolism is abnormal in schizophrenic patients. Our own studies, consistent with those of other research groups, have shown marked depletion of essential fatty acids, particularly arachidonic acid and docosahexanoic acid, in red blood cell membranes from schizophrenic patients relative to healthy control subjects. We also present preliminary evidence that similar abnormalities are present in first degree relatives of schizophrenic patients. Furthermore, it appears that changes in diet, which modify membrane levels of fatty acids, can have significant effects upon symptoms of schizophrenia and tardive dyskinesia (TD). Thus, we have found that schizophrenic patients who eat more (n-3) fatty acids in their normal diet have less severe symptoms. In a pilot study of (n-3) fatty acid supplementation we observed significant improvement in both schizophrenic symptoms and tardive dyskinesia over a 6 week period.

Purification of chlorpromazine-sensitive GTPase from rat cerebral cortex

The chlorpromazine-sensitive GTPase from the cell membrane of rat cerebral cortex was purified to homogenity by using DEAE Bio-Gel A agarose, hydroxyapatite and heparin agarose chromatography. The purified chlorpromazine-sensitive GTPase was purified 370-fold to obtain a final specific activity of 40 mumol GTP hydrolyzed2min/mg protein. The purified enzyme was inhibited by chlorpromazine but not by compound 48/80. Magnesium was required for its activity instead of calcium. The purified enzyme had an apparent pH optimum of 8.0, and molecular weight was estimated to be 58,000.

Effect of chlorpromazine on the synthesis of neutral lipids and phospholipids from [3H]glycerol in the primordial human placenta

Addition of chlorpromazine (CPZ) of 100 microM final concentration to fragments of primordial human placenta incubated in vitro with [3H]glycerol results in the following changes in the labelling of various neutral lipids and phospholipids: (1) rapid accumulation of [3H]phosphatidic acid (PA) to a 2.31 +/- 0.12-fold (mean +/- s.d., P < 0.05) higher steady-state level within 5 min; (2) a dramatic, 5-6-fold (5.74 +/- 0.31, P < 0.01) increase in [3H]phosphatidylinositol (PI) synthesis within 5-10 min, followed by progressive PI accumulation; (3) gradual accumulation of [3H]1,2-diacylglycerol (DAG) reaching approximately 1.7-fold (1.72 +/- 0.14, P < 0.05) higher steady-state level at 30 min; and (4) an approximately 20 and 30% decrease in [3H]triacylglycerol (TG) and [3H]phosphatidylcholine (PC) formation, respectively, which begins to become evident between 10-30 min. As dose-response studies indicate, accumulations of PI and DAG are most susceptible to CPZ. They respond in the concentration range of 10-50 microM, while only higher drug concentrations (100-250 microM) affect the synthesis of PA, PC and TG significantly. Finally, dioctanoylethyleneglycol (DOEG), a structural analogue of the diacyl moiety of PA and DAG, selectively inhibits the basal synthesis (0.59 +/- 0.15, P < 0.05) as well as the CPZ-induced rise (0.49 +/- 0.11, P < 0.02) of PI. These results suggest that CPZ-induced increase in the concentrations of PI and 1,2-DAG may interfere with signal-transduction pathways in the placenta of pregnant patients treated with CPZ. Furthermore, DOEG is able to antagonize the CPZ effect which directs lipid biosynthesis towards the formation of PI.

Thapsigargin selectively stimulates synthesis of phosphatidylglycerol in N1E-115 neuroblastoma cells and phosphatidylinositol in C6 glioma cells

Phospholipid metabolism was studied in N1E-115 neuroblastoma and C6 glioma cells exposed to thapsigargin, a selective inhibitor of endoplasmic reticulum Ca(2+)-ATPase that raises the cytosolic free Ca2+ concentration [Ca2+]i. Thapsigargin caused only a transient increase of [Ca2+]i (< 1 min) in N1E-115 cells similar in magnitude and duration to agonist-induced calcium release mediated by inositol trisphosphate. Sustained elevation of [Ca2+]i due to influx of extracellular calcium, as occurs in most other cell lines including C6 cells, did not occur in N1E-115 cells. Increased uptake of inorganic phosphate (Pi) associated calcium influx was observed in C6 but not in N1E-115 cells. Thapsigargin affected phospholipid synthesis in both cell lines, most likely by inhibiting phosphatidic acid phosphohydrolase as indicated by diversion of [3H]oleic acid incorporation from triacylglycerol to phospholipid synthesis and stimulation of [32P]Pi incorporation into anionic phospholipids at the expense of phosphatidylcholine synthesis. The response to increased phosphatidate/phosphatidyl-CMP availability was cell specific. Thapsigargin (> 100 nM) selectively stimulated phosphatidylglycerol synthesis 20-30-fold in N1E-115 neuroblastoma cells while phosphatidylinositol synthesis was increased < 2-fold. In contrast, phosphatidylglycerol was not affected in C6 glioma cells and phosphatidylinositol synthesis was stimulated 8-fold by thapsigargin (> 1 microM). Agonist-stimulated calcium release did not increase phosphatidylglycerol synthesis in N1E-115 cells. Thapsigargin-stimulated phosphatidylglycerol synthesis and agonist-stimulated phosphatidylinositol synthesis could occur at the same time. Similar results were obtained with TMB-8, an inhibitor of intracellular Ca2+ release that decreases diacylglycerol utilization by blocking choline uptake and phosphatidylcholine synthesis without affecting resting [Ca2+]i. Thus [Ca2+]i does not directly mediate the effects of thapsigargin, TMB-8 or agonist stimulation on anionic phospholipid metabolism. These additional effects may limit the use of thapsigargin to assess Ca(2+)-dependence of phospholipid metabolism associated with Ca(2+)-mediated signal transduction.

Effects of perphenazine on the metabolism of inositol phospholipids in SK-N-BE(2) human neuroblastoma cells

Administration of myo-[3H]inositol to SK-N-BE(2) human neuroblastoma cells for 24 hr resulted in equilibrium labelling of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2), as well as in retention of a large intracellular pool of free myo-[3H]inositol. Equilibrium labelling was no longer observed when cells were treated for 2 hr with 20 microM perphenazine (PPZ) in label-free medium; under these conditions, myo-[3H]inositol from the retained intracellular pool was incorporated into PI and PIP but not into PIP2. Analysis of water-soluble myo-[3H]inositol derivatives and inositol 1,4,5-trisphosphate mass determination indicated that PPZ did not stimulate phosphoinositide hydrolysis by phospholipase C. These results indicate that PPZ raises PI and PIP levels, whereas it is ineffective in expanding the PIP2 pool. The latter effect is not due to a concomitant synthesis and hydrolysis of this lipid.

The tricyclic antidepressant desipramine causes proteolytic degradation of lysosomal sphingomyelinase in human fibroblasts

The effect of the tricyclic antidepressant desipramine on the processing of lysosomal sphingomyelinase (EC 3.1.4.12) was investigated by pulse-chase studies on [35S]methionine labeled cultured human skin fibroblasts. Desipramine induced rapid intracellular degradation of mature acid sphingomyelinase when added to the cells in the micromolar range, concomitantly abolishing the enzyme activity. Pulse chase labeling revealed the disappearance of mature enzyme forms when fibroblasts were treated with 25 microM desipramine. Incubation of cells with 25 microM leupeptin, an inhibitor of thiol proteases, 24 h prior to desipramine intoxication prevented this drug-induced effect. From these results we conclude that desipramine and possibly also similarly acting tricyclic antidepressants induce proteolytic degradation of acid sphingomyelinase.

Effect of chloroquine on mast cell membranes

The effect of chloroquine (CQ) on phospholipid turnover and de novo synthesis in isolated rat mast cells (IRMC) was studied by determining the incorporation of 32P and 14C-glycerol into IRMC phospholipids. Incubation of mast cells with chloroquine increased 32P incorporation into PI and PS whilst it decreased 32P incorporation into PC, PE and PA. In mast cells pretreated with CQ and subsequently stimulated with compound 48/80, 32P incorporation into PI, PS and PA fractions was enhanced, while it was decreased into PC and PE, in comparison to 48/80 stimulated IRMC. 14C-glycerol incorporation into total IRMC phospholipids was not significantly changed by CQ and compound 48/80 treatment and neither was any dose-dependent effect of CQ on individual phospholipids detected. Our results indicate that chloroquine, similarly to other cationic amphiphilic drugs, may alter membrane PL turnover without changing de novo synthesis of phospholipids.

Ca2+ release from inositol 1,4,5-trisphosphate-sensitive Ca2+ store by antidepressant drugs in cultured neurons of rat frontal cortex

The ability of antidepressant drugs (ADs) to increase the concentration of intracellular Ca2+ ([Ca2+]i) was examined in primary cultured neurons from rat frontal cortices using the Ca(2+)-sensitive fluorescent indicator fura-2. Amitriptyline, imipramine, desipramine, and mianserin elicited transient increases in [Ca2+]i in a concentration-dependent manner (100 microM to 1 mM). These four AD-induced [Ca2+]i increases were not altered by the absence of external Ca2+ or by the presence of La3+ (30 microM), suggesting that these ADs provoked intracellular Ca2+ mobilization rather than Ca2+ influx. All four ADs increased inositol 1,4,5-trisphosphate (IP3) contents by 20-60% in the cultured cells. The potency of the IP3 production by these ADs closely correlated with the AD-induced [Ca2+]i responses. Pretreatment with neomycin, an inhibitor of IP3 generation, significantly inhibited amitriptyline- and imipramine-induced [Ca2+]i increases. In addition, by initially perfusing with bradykinin (10 microM) or acetylcholine (10 microM), which can stimulate the IP3 generation and mobilize the intracellular Ca2+, the amitriptyline responses were decreased by 76% and 69%, respectively. The amitriptyline-induced [Ca2+]i increases were unaffected by treatment with pertussis toxin. We conclude that high concentrations of amitriptyline and three other ADs mobilize Ca2+ from IP3-sensitive Ca2+ stores and that the responses are pertussis toxin-insensitive. However, it seems unlikely that the effects requiring high concentrations of ADs are related to the therapeutic action.

Phenothiazines inhibit acetylcholinesterase by concentration-dependent-type kinetics. A study with trifluoperazine and perphenazine

The properties of perphenazine (PPZ) and trifluoperazine (TFP) as fluorescent dyes were exploited to calculate their critical micellar concentrations. The relative fluorescence quantum yield of the two amphiphiles was dependent on their concentration, abruptly decreasing above 30-40 microM PPZ and 20-30 microM TFP. Evidence is presented that this phenomenon is driven by the formation of non-fluorescent drug aggregates. The type of inhibition kinetics displayed by PPZ and TFP on human erythrocyte acetylcholinesterase (AChE) was also dependent on drug concentration, turning from non-competitive to a "mixed" inhibition type at concentrations at which PPZ and TFP were demonstrated to undergo micelle formation. Results support the notion that phenothiazines may interact with AChE both as monomers and micellar aggregates, producing different inhibitory effects.

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

TMB-8 [8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate] blocks agonist-stimulated release of Ca2+ from intracellular sites in many cell lines and is often used to distinguish between dependence on extracellular and intracellular Ca2+. In N1E-115 neuroblastoma cells, TMB-8 did not alter the resting cytosolic Ca2+ concentration in unstimulated cells, yet phospholipid metabolism was greatly affected. At concentrations of TMB-8 (25-150 microM) that inhibit Ca2+ release, phosphatidylcholine formation was inhibited, whereas synthesis of phosphatidylinositol, phosphatidylglycerol and phosphatidylserine was stimulated. Unlike other cationic amphipathic compounds, TMB-8 did not inhibit phosphatidate phosphatase or enzymes in the pathway from choline to phosphatidylcholine. Choline transport was the major site of action. TMB-8 was a competitive inhibitor (Ki = 10 microM) of low-affinity (Kt = 20 microM) choline transport. When added at the same time as labelled precursor, TMB-8 also decreased cellular uptake of phosphate and inositol, but not that of ethanolamine or serine. In prelabelled cells, continued uptake and incorporation of phosphate and inositol were not affected. Under these conditions phosphatidylinositol synthesis was increased 2-fold and, like the effect on phosphatidylcholine, reached a plateau at 100 microM-TMB-8. Phosphatidylglycerol synthesis increased linearly with TMB-8 concentration to 40-fold stimulation at 150 microM, suggesting a selective effect on synthesis of phosphatidylglycerol from CDP-diacylglycerol. Phosphatidylserine synthesis was also increased up to 3-fold. These Ca(2+)-independent effects limit the use of TMB-8 in studies of cell signalling that involve stimulated phosphatidylinositol and phosphatidylcholine metabolism.

Age-dependent changes in receptor-stimulated phosphoinositide turnover in the rat hippocampus

To study the changes in the hippocampal cholinergic system of chronologically old and behaviorally impaired animals, old (21 months of age) and young (3 months of age) male, Fischer-344 rats were used. The aged animals were tested on a reference memory task (Morris water maze) and found to be functionally impaired as compared to the young controls. Carbachol-stimulated phosphoinositide metabolism was measured in hippocampal slices from young and old rats. Slices were prelabeled with 3H-inositol for 120 min and subjected to muscarinic stimulation in the presence of lithium. Following extraction of the slices with acidified solvent mixture, the inositolphosphates present in the aqueous fraction were isolated by ion exchange chromatography. Receptor-stimulated release of inositolphosphates (IPs) was found to be increased in the hippocampus of older animals. This age-related enhancement of IP release was in contrast to the decrease in choline acetyltransferase (CHAT) activity in the hippocampus. We postulate that alterations in the G-protein coupling with the muscarinic receptor leads to an increase in the phosphoinositide turnover in part as a compensatory mechanism for neuronal cell death and reduced transmitter levels.

Inhibition of phosphatidic acid phosphohydrolase activity by sphingosine. Dual action of sphingosine in diacylglycerol signal termination

Recent evidence indicates that a major fraction of diacylglycerol that is produced in hormonally stimulated cells arises by phosphatidylcholine hydrolysis via the sequential action of phospholipase D and phosphatidic acid phosphohydrolase (PAP). We have previously reported that sphingoid bases stimulate phospholipase D activity in NG108-15 cells. The evidence presented here demonstrates that in sphingosine-treated NG108-15 cells, elevated phosphatidic acid levels are accompanied by a parallel, time- and dose-dependent decrease in diacylglycerol levels. DL-propranolol, a known inhibitor of PAP, exerted similar effects, suggesting that the action of sphingosine may have been due to inhibition of PAP activity. This prediction was confirmed in in vitro experiments in which it was demonstrated that sphingosine is as potent an inhibitor of both cytosolic and membrane-associated PAP activity as propranolol. The hypothesis that sphingoid bases may exert a dual action in diacylglycerol signal termination is proposed.

Effect of desipramine on a glycoprotein sialyltransferase activity in C6 cultured glioma cells

The tricyclic antidepressant desipramine, when added to culture medium, gave rise in C6 rat glioma cells to a decrease of the activity of the enzyme asialofetuin sialyltransferase. The inhibition was dose and time dependent and was observed in both multiplying cells and cells blocked with 2 mM thymidine or depletion of amino acids. This inhibition was rather specific to the sialyltransferase, as under the conditions where this enzyme was inhibited up to 70%, other enzymes such as dolichol phosphate mannose synthetase, glutamine synthetase, and glycerol phosphate dehydrogenase remained unaffected. This inhibition was not reversed after removal of desipramine from the medium and was not observed by direct addition of desipramine to the sialyltransferase incubation assay. Under the same conditions, W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide], which is known to be a potent calmodulin antagonist and an inhibitor of calmodulin-dependent kinases, gave the same concentration-dependent inhibition profile of sialyltransferase as desipramine, whereas H-7 [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine], which is an inhibitor of protein kinase C and cyclic nucleotide-dependent kinases, had no effect. So, it is suggested that desipramine inhibits the sialyltransferase activity in C6 glioma cells through a calmodulin-dependent system.

Accumulation of inositol phosphates induced by chlorpromazine in C6 glioma cells

Chlorpromazine, a cationic amphiphilic drug known to affect phospholipid metabolism, greatly increases the generation of inositol phosphates in C6 glioma cells. When a pulse-chase protocol with myo-[2-3H]inositol as the radioactive precursor was used, the peak increase in radioactivity of inositol phosphates was observed at 20 min. The drug decreased inositol tetrakisphosphate labeling as a percentage of inositol trisphosphate in a dose-dependent manner. It also increased the labeling of the inositol-containing phospholipids, the precursors of the inositol phosphates. The increase in radioactivity of both phospholipids and inositol phosphates was dose-dependent, but appeared also to be a function of the time of exposure of the cultures to the drug, suggesting that the concentration of chlorpromazine in the cell, and not that in the medium, is the critical factor. The optimum concentration for maximum phospholipid labeling was lower than that eliciting maximum generation of inositol phosphates. The data suggest that the mechanism probably does not involve cell-surface receptors, but rather may consist of a direct effect of chlorpromazine on phosphoinositidase C and possibly other enzymatic reactions concerned with the metabolism of inositol phosphates.

Phosphatidylinositol kinase of bovine adrenal chromaffin granules. Modulation by hydrophilic and amphiphilic cations

The effects of hydrophilic and amphiphilic cations on the activity of phosphatidylinositol (PI) kinase (EC 2.7.1.67) of chromaffin granule ghosts were investigated. The cations studied can be divided into two groups, i.e. (i) compounds with a biphasic response (stimulation and inhibition), and (ii) those with a selective stimulatory effect on the enzyme activity. The cationic amphiphile trifluoperazine belongs to the first group, and stimulated the enzyme activity, maximal at 80 microM (2-fold), with a progressive inhibition at higher concentrations. This biphasic response was shared by a number of structurally related cationic amphiphiles, i.e. the tricyclic antidepressants, imipramine and desipramine, the phenothiazine, chlorpromazine, the miconazole derivative, calmidazolium, the beta-adrenergic agonist, propranolol, compound 48/80, as well as by the hydrophilic cations neomycin and poly-L-lysine. On the other hand, a pure stimulatory effect was observed with the amphiphilic polypeptide mastoparan and the polycationic compound spermidine, whereas ACTH1-39 and ACTH1-24 (peptides structurally related to mastoparan) revealed a slight inhibitory effect. We conclude that all the cations tested including Mg2+, stimulate PI kinase activity rather unspecifically by binding of the positively charged groups to a membrane component, probably the PI kinase itself. This site is different from that mediating the specific inhibition by calcium (Husebye ES and Flatmark T, Biochim Biophys Acta 968: 261-265, 1988). The inhibitory effect of cationic amphiphiles is correlated to their lipid solubility, and represents a perturbation of the membrane structure, but not a solubilization of enzyme or phosphoinositide from the membrane. The inhibitory effect of hydrophilic cations is due to complexation of ATP.

Differential effects of chloroquine on the phospholipid metabolism of Plasmodium-infected erythrocytes

The effect of the antimalarial drug chloroquine (CQ) on the phospholipid metabolism in Plasmodium knowlesi-infected simian erythrocytes has been studied by incubating cells with different labeled precursors and various concentrations of CQ. The drug induced considerable modifications of this metabolism but at the same time decreased nucleic acid and protein synthesis as well as the output of 14CO2 from radioactive glucose. Phosphatidylcholine biosynthesis was severely reduced. However, under these conditions, CQ had the early effect of markedly increasing phosphatidylinositol labeling from radioactive inositol, fatty acids, 1-(14C)palmitoyl-lysophosphatidylcholine, but not from glycerol. Synthesis of phosphatidylserine from (14C)serine and of phosphatidylethanolamine from labeled glycerol, ethanolamine, and serine was increased, especially at high CQ concentrations when the whole metabolism of the parasite was severely reduced. These effects reflect a deep differential effect of CQ on the intense phospholipid metabolism of the Plasmodium-infected erythrocytes, which might involve a redirecting of phospholipid metabolism similar to that induced by other cationic amphiphilic drugs, and a compensatory synthesis resulting from the severe blockage of phosphatidylcholine synthesis.

In vitro and ex vivo effects of antidepressants on rat brain membrane-bound phosphatidylinositol synthetase activity

The in vitro and ex vivo effects of antidepressant drugs on membrane-bound phosphatidylinositol (PI) synthetase and PI: myo-inositol exchange enzyme activities were examined. In rat brain subcellular fractions, PI synthetase occurred exclusively in the microsomes. In comparison, the activity of CDP-diglyceride independent PI:myo-inositol exchange enzyme was low (3%). Of the various CDP-diglycerides tested for the activation of PI synthetase, CDP-dipalmitin was the most active. Addition of 1 mM of desipramine, amitriptyline, imipramine, iprindole, clomipramine and mianserin in vitro significantly inhibited (30-60%) PI synthetase activity, whereas the same concentration of zimelidine and fluoxetine had no effect. At low liponucleotide concentrations, PI synthetase activity was significantly enhanced by imipramine (1 mM), whereas the enzyme activity was inhibited at higher liponucleotide concentrations (greater than 0.3 mM). In contrast, imipramine had no effect on the PI: myo-inositol exchange enzyme activity. No significant alteration in the PI synthetase activity was found following either acute (2 h) or chronic (21 d) treatment of rats with imipramine. The above results indicate that the de novo synthesis of PI is inhibited in vitro but not ex vivo by some antidepressant drugs. However, in view of the high concentration of the drugs required, the pharmacological significance of this inhibitory action with respect to their therapeutic effects is doubtful.