The metabolism of CDP-diacylglycerol and phosphatidylinositol in the microsomal fraction of rat liver. Effects of chlorpromazine, magnesium and manganese

Regulation of cardiolipin biosynthesis in the heart

Cardiolipin is one of the principle phospholipids in the mammalian heart comprising as much as 15-20% of the entire phospholipid phosphorus mass of that organ. Cardiolipin is localized primarily in the mitochondria and appears to be essential for the function of several enzymes of oxidative phosphorylation. Thus, cardiolipin is essential for production of energy for the heart to beat. Cardiac cardiolipin is synthesized via the cytidine-5'-diphosphate-1,2-diacyl-sn-glycerol pathway. The properties of the four enzymes of the cytidine-5'-diphosphate-1,2-diacyl-sn-glycerol pathway have been characterized in the heart. The rate-limiting step of this pathway is catalyzed by the phosphatidic acid: cytidine-5'-triphosphate cytidylyltransferase. Several regulatory mechanisms that govern cardiolipin biosynthesis in the heart have been uncovered. Current evidence suggests that cardiolipin biosynthesis is regulated by the energy status (adenosine-5'-triphosphate and cytidine-5'-triphosphate level) of the heart. Thyroid hormone and unsaturated fatty acids may regulate cardiolipin biosynthesis at the level of three key enzymes of the cytidine-5'-diphosphate-1,2-diacyl-sn-glycerol pathway, phosphatidylglycerol phosphate synthase, phosphatidyl-glycerolphosphate phosphatase and cardiolipin synthase. Newly synthesized phosphatidic acid and phosphatidylglycerol may be preferentially utilized for cardiolipin biosynthesis in the heart. In addition, separate pools of phosphatidylglycerol, including an exogenous (extra-mitochondrial) pool not derived from de novo phosphatidylglycerol biosynthesis, may be utilized for cardiac cardiolipin biosynthesis. In several mammalian tissues a significant number of studies on polyglycerophospholipid biosynthesis have been documented, including detailed studies in the lung and liver. However, in spite of the important role of cardiolipin in the maintenance of mitochondrial function and membrane integrity, studies on the control of cardiolipin biosynthesis in the mammalian heart have been largely neglected. The purpose of this review will be to briefly discuss cardiolipin and cardiolipin biosynthesis in some selected model systems and focus primarily on current studies involving the regulation of cardiolipin biosynthesis in the heart.

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.

Subcellular distribution of (+)-[3H]SKF 10,047 binding sites in rat liver

The distribution of (+)-[3H]SKF 10,047 binding sites and the distribution of the established plasma membrane, nuclear, mitochondrial and endoplasmic reticulum markers in subcellular fractions of rat liver have been studied. The distribution profile of (+)-[3H]SKF 10,047 binding sites coincided with that of NADPH-cytochrome c reductase, the endoplasmic reticulum marker. (+)-[3H]SKF 10,047 binding sites in rat liver are therefore suggested to be located on the endoplasmic reticulum membrane and to represent a membrane-bound enzyme.

Phosphatidylinositol synthetase activities in neuronal nuclei and microsomal fractions isolated from immature rabbit cerebral cortex

The synthesis of phosphatidylinositol was studied using a nuclear fraction N1, a microsomal fraction P3, rough (R) and smooth (S) microsomal fractions and a microsomal fraction P derived from isolated nerve cell bodies. Each fraction was prepared using cerebral cortices of 15-day-old rabbits. In assays using CDP-diacylglycerol (prepared from egg phosphatidylcholine) and myo[3H]inositol at pH 7.4, fraction N1 had the highest maximal specific rates of phosphatidylinositol synthetase (EC 2.7.8.11) (expressed per mumol phospholipid in the fraction). However the three microsomal fractions achieved maximal specific activities at liponucleotide concentrations close to 50 microM, while fraction N1 required 200 microM concentrations. In certain cases (25-120 microM CDP-diacylglycerol, and at higher pH values) fraction R had specific activities which equalled or surpassed those of N1. However, with respect to inositol, fraction N1 had a distinctly lower Km than was shown for fractions R or P3. Each of the microsomal fractions and N1 required Mg2+ for the reaction, but for N1, maximal rates could be sustained at 0.1 mM, while for the microsomal fractions the optimal Mg2+ concentration was 1 mM. For each fraction Mn2+ could not replace Mg2+ in the reaction and Mn2+ was inhibitory. The optimal pH for the reaction was between 8.0 and 9.0. Phosphatidylinositol synthetase could also be shown using fraction N1 enriched in endogenous CDP-diacylglycerol. The relatively high specific activities of fraction N1, and the differences found between N1 and the microsomal fractions, for optimal CDP-diacylglycerol and Mg2+ concentrations and for Km values for inositol, support the existence of a neuronal nuclear phosphatidylinositol synthetase.

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.

Comparison of the HPLC-separated species patterns of phosphatidic acid, CDP-diacylglycerol and diacylglycerol synthesized de novo in rat liver microsomes (a new method)

The species pattern of phosphatidic acid was compared with that of CDP-diacylglycerol and diacylglycerol synthesized de novo by glycerol 3-phosphate acylation in a CoA ester-generating system in liver microsomes. The similarity of the species patterns of phosphatidic acid and CDP-diacylglycerol indicated that the CTP-phosphatidyl cytidylyltransferase showed no selectivity for individual species of its phosphatidic acid substrate. Since the species pattern of diacylglycerol deviated from that of phosphatidic acid, a slight acyl selectivity of the phosphatidic acid phosphohydrolase or a slight inhomogeneity of its substrate pool might be assumed. For the determination of the molecular species of CDP-diacylglycerol, a new method was developed. By incubation of CDP-diacylglycerol with oligonucleate 5'-nucleotidohydrolase (phosphodiesterase), phosphatidic acid was produced. The CDP-diacylglycerol-derived phosphatidic acid was methylated with diazomethane and then separated by reverse-phase HPLC in 15 molecular species.

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.

Trifluoperazine increases fatty acid turnover in phospholipids in cultured human fibroblasts

A 24-hr pretreatment of cultured human fibroblasts with trifluoperazine induced a marked increase in incorporation of saturated (stearic, palmitic) and unsaturated (oleic, arachidonic) fatty acids into phospholipids (1.5- to 2-fold for 5.10(-5) M trifluoperazine). Concomitantly, incorporation into cholesteryl esters was strongly inhibited (20% of control for 5.10(-5) M trifluoperazine). The drug did not change the phospholipid composition of treated cells. The effect of trifluoperazine on oleic acid incorporation into phospholipids was time-dependent and reached a maximum after a six-hr preincubation with the drug. Trifluoperazine also induced an increase in the rate of chase of oleic acid from the different phospholipid classes. In vitro preincubation of cell-free extracts with trifluoperazine resulted in activation of phospholipid acyltransferases, whereas cholesterol acyltransferase activity was decreased. The rapid effect of trifluoperazine together with its effect on a cell-free system suggests a direct action of this amphiphilic drug on the acyltransferase activities, probably by modification of the structural organization of cellular membranes.

Differential effect of progesterone on the labeling of phosphatidylinositol with [3H]inositol and [32P]phosphate in the uterus of the estrogen-treated ovariectomized rat

In rat uterine mince incubated in vitro [3H]inositol was found to be incorporated into phosphatidylinositol (PI) predominantly via a pathway which could be markedly and dose dependently activated with Mn2+ (0.1-10 mM) and inhibited by Ca2+ (1-10 mM). These ions had no effect on the incorporation of [32P]phosphate (32P) into PI indicating a distinct inositol-exchange mechanism for the labeling of PI with [3H]inositol. Treatment of ovariectomized rats for 5 days with 2 micrograms estradiol dipropionate (EDP) increased about 3-fold (when measured in the presence of 1 mM Mn2+) and 4-5-fold (when measured in the presence of 1 mM Ca2+) the inositol-exchange activity in the rat uterus, and these effects were suppressed by 40 and 30% respectively by the concomitant administration of 2 mg progesterone (P). EDP alone or in combination with P increased to the same extent (by a factor of 2-3) the rate of labeling with 32P of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and plasmenylethanolamine (PmE). The labeling rate of PI was increased 1.5-1.7-fold by treatment with EDP and this increase was selectively augmented further to about 2.5-fold by the simultaneous administration of P. Treatment with P alone had no significant effect on the incorporation of either labeled precursor. Steroid hormone treatments had no effect on the amount of these phospholipids in 100 mg uterine tissue, but they increased about 1.7-fold the rate of labeling of ATP with 32P. We conclude that P, when administered together with estradiol, regulates differentially the turnover of the inositol and phosphate moieties of PI with possible physiological consequences.

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

The effects of chlorpromazine (CPZ), desmethylimipramine (DMI) and propranolol (PRO) on phospholipid metabolism in C6 glioma cells were studied by following the incorporation of 32Pi, [U-14C]glycerol, [2-3H]glycerol and [1-14C]oleate into lipids. The drugs produced a dose-dependent increase in the incorporation of 32Pi and [U-14C]glycerol, but not of [1-14C] oleate, into total phospholipids, that reached a plateau at 200 microM CPZ and 500 microM DMI and PRO. The three drugs shifted the incorporation of precursors from neutral [phosphatidylcholine (PC) and phosphatidylethanolamine (PE)] to acidic phospholipids [phosphatidic acid (PA), phosphatidylinositol (PI), phosphatidylglycerol, phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2)] in a dose-dependent, qualitatively similar manner. The incorporation of [2-3H]glycerol into diacylglycerol was also depressed markedly by CPZ. Addition of 1 mM 1,2-dioleoylglycerol, 1-oleoyl-2-acetylglycerol or oleate only partially reversed the decrease in PC labeling caused by CPZ. 12-O-Tetradecanoylphorbol-13-acetate counteracted this effect of CPZ completely but greatly increased PC labeling even in the absence of the drug. Polyphosphoinositides rapidly incorporated 32Pi at early times reaching a plateau in about 40 min. The labeling rate of PI was not parallel to that of PIP or PIP2 and continued to increase even after the polyphosphoinositides had reached a plateau. CPZ increased PI labeling much more than that of PIP and PIP2. These data suggest that cationic amphiphilic drugs may act by inhibiting CTP:phosphocholine cytidylyltransferase, thus decreasing incorporation of precursors into PC and PE; inhibiting PA phosphohydrolase with increased formation of phosphatidyl-CMP, the intermediate for the synthesis of acidic phospholipids; and stimulating the inositol exchange reaction, forming a pool of PI that is not available for PIP and PIP2 synthesis.

In vitro effects of chlorpromazine on glycerol-3-phosphate acyl transferase and 1-acylglycerol-3-phosphate acyltransferase in rat liver microsomes

The in vitro effect of chlorpromazine on rat liver glycerol-3-phosphate acyltransferase and 1-acylglycerol-3-phosphate acyltransferase was studied. Chlorpromazine decreased glycerol-3-phosphate acyltransferase activity in a concentration-dependent manner. The inhibition was competitive with respect to palmitoyl-CoA, while non-competitive with respect to sn-glycerol-3-phosphate. Ki was determined to be approximately 0.15 mM with respect to both palmitoyl-CoA and sn-glycerol-3-phosphate. From these results, together with the inhibitory effect of amphiphilic anions and neutral detergents on the enzyme demonstrated by others, it was proposed that the hydrophobic moiety of chlorpromazine competes with acyl-CoA. The activity of 1-acylglycerol-3-phosphate acyltransferase was inhibited by excess of 1-acyl-sn-glycerol-3-phosphate. In the acceptor concentration range where the substrate inhibition was observed, chlorpromazine showed stimulatory effect on the enzyme activity. At lower concentrations of the acceptor, however, chlorpromazine produced marked inhibition of the enzyme activity. From the kinetic analysis, the inhibition was found to be uncompetitive with respect to acyl-CoA. It was found that the enzyme was more susceptible to the inhibitory action of chlorpromazine with unsaturated acyl-CoAs than with the saturated species, raising the possibility that chlorpromazine alters the molecular species composition of phosphatidic acid produced by the acylation reaction.

Differential effects of chlorpromazine on secretion, protein phosphorylation and phosphoinositide metabolism in stimulated platelets

Increasing concentrations of chlorpromazine (30-500 microM) caused a progressive lysis of gel-filtered platelets, as monitored by the extracellular appearance of cytoplasmic ([14C]adenine-labelled) adenine nucleotides. The chlorpromazine-induced lysis was markedly enhanced by thrombin and phorbol ester, and complete cytolysis was found at chlorpromazine concentrations of 100 microM and above in the presence of thrombin. At non-lytic concentrations, chlorpromazine caused a dramatic increase in the thrombin- or phorbol ester-mediated incorporation of 32P into phosphatidylinositol 4-phosphate and, to a lesser extent, into phosphatidylinositol 4,5-bisphosphate in platelets pulse-labelled with [32P]Pi. Chlorpromazine alone also caused an incorporation of 32P into the phosphoinositides. Non-lytic concentrations of chlorpromazine had no effect on the phosphorylation of the 47 kDa protein (regarded as the substrate for protein kinase C), but markedly inhibited the accompanying secretion of ATP + ADP and beta-hexosaminidase when platelets were incubated with 0.17 microM-phorbol ester or 0.1-0.2 unit of thrombin/ml. At lower concentrations of thrombin, chlorpromazine did not inhibit, but slightly enhanced, secretion. A protein of 82 kDa was phosphorylated during the interaction of platelets with thrombin and phorbol ester, and this phosphorylation was enhanced by chlorpromazine (non-lytic). These results suggest that the previously reported inhibition of protein kinase C by chlorpromazine is probably non-specific and due to cytolysis. However, since non-lytic concentrations of chlorpromazine inhibit secretion, but not protein kinase C, in platelets, activation of protein kinase C is not involved in the stimulation-secretion coupling, or chlorpromazine acts at a step after kinase activation. Possible mechanisms of this inhibition by chlorpromazine are discussed in the light of its effect on phosphoinositide metabolism and protein phosphorylation.

Chlorpromazine induces accumulation of inositol phosphates in C6 glioma cells

The capacity to modify the incorporation of [2-3H]myo-inositol into inositides and inositol phosphates was different for three psychotropic cationic amphiphilic drugs. Chlorpromazine, desmethylimipramine and propranolol were able to increase the labeling of inositol-containing lipids, but only chlorpromazine dramatically increased the incorporation into inositol phosphate, -bisphosphate and -trisphosphate. The increase was 10- to 50-fold in 60 min as compared with controls. This effect is not due to stimulation of lipid labeling, because in chase experiments radioactivity in inositol phosphates increased to a greater extent than in their parent lipids. It is possible that the alteration of phosphoinositide catabolism is related to the neuroleptic activity of the drug.

Metabolism of phosphatidyl-dCMP in sarcoma 180 cells. Effect of chlorpromazine, phosphatidic acid and inositol

The synthesis and degradation of phosphatidyl-dCMP was studied in intact and permeabilized Sarcoma 180 cells as well as in isolated nuclei. It was verified that chlorpromazine greatly enhanced phosphatidyl-dCMP synthesis and completely abolished its hydrolysis in intact cells. The former effect was reversible and was partially lost upon permeabilization or isolation of nuclei. Phosphatidic acid also increased liponucleotide synthesis and the combination of phosphatidic acid with chlorpromazine was not additive. When inositol was added to cells which had accumulated phosphatidyl-[3H]dCMP, the recovery of radioactivity in the organic phase decreased; this effect was dose-dependent and specific for inositol, and was accompanied by an increased release of [3H]dCMP to the cell medium. In isolated microsomes, addition of Ptd-dCMP determined incorporation of [3H]inositol into phosphatidyl-inositol. These results strongly suggest that phosphatidyl-dCMP is utilized for the synthesis of phosphatidyl-inositol.

Effect of chlorpromazine associated with liposomes on the biosynthesis of acidic lipids in subcellular membranes

The study examined the effect of an association of chlorpromazine, phosphatidic acid and cytidine-diphosphoryl-1,2-diglycerides (CDP-diglycerides) with small unilamellar lecithin liposomes on the formation, hydrolysis and transfer of lipids and cytidine liponucleotides in microsomal and mitochondrial membranes isolated from guinea-pig liver. Association with liposomes undermined the effect of chlorpromazine on these processes, but the type of effect, i.e. inhibitory or stimulatory, was retained. Association of CDP-diglycerides with small unilamellar lecithin liposomes tended to protect this substrate from subcellular uptake, thereby inhibiting phosphatidylinositol and polyglycerophosphatide formation. Phosphatidic acid in the form of liposomes stimulated CDP-diglyceride formation. The nature of fatty acids influenced the magnitude of these effects in polyglycerophosphatide biosynthesis. Transfer of CDP-diglycerides from microsomal to mitochondrial membranes was inhibited by both chlorpromazine associated with liposomes and liposomes alone.

Trifluoperazine and chlorpromazine inhibit phosphatidylcholine biosynthesis and CTP:phosphocholine cytidylyltransferase in HeLa cells

The influence of chlorpromazine and trifluoperazine on phosphatidylcholine biosynthesis in HeLa cells was investigated. HeLa cells were prelabeled with [Me-3H]choline for 1 h. The cells were subsequently incubated with various concentrations of drugs. Both compounds were potent inhibitors of phosphatidylcholine biosynthesis, with 50% inhibition by 5 micron of either drug. Analysis of the radioactivity in the soluble precursors indicated a block in the conversion of phosphocholine to CDPcholine catalyzed by CTP:phosphocholine cytidylyltransferase (CTP:cholinephosphate cytidylyltransferase, EC 2.7.7.15). Inhibition by these drugs was slowly reversed after incubation for more than 2 h, or was immediately abolished when 0.4 mM oleate was included in the cell medium or when the drug-containing medium was removed. The subcellular location of the cytidylyltransferase was unaffected by either drug, nor did the drugs alter the rate of release of cytidylyltransferase from HeLa cells by digitonin treatment. The drugs had a direct inhibitory effect on cytidylyltransferase activity in HeLa cell postmitochondrial supernatants. Half-maximal inhibition was achieved with 30 microM trifluoperazine and 50 microM chlorpromazine. These drugs did not change the apparent Km of the cytidylyltransferase for CTP or phosphocholine. Inhibition of cytidylyltransferase by these compounds was reversible with exogenous phospholipid or oleate in the enzyme assay. The data indicate that both drugs inhibit phosphatidylcholine synthesis by an effect on the cytidylyltransferase. The mechanism of action remains unknown at this time.

Effect of nucleotides on the incorporation of myo-inositol into phosphatidylinositol in rat liver microsomes

In rat liver microsomes the incorporation of inositol in the presence of Mn2+ was stimulated by cytidine nucleotides, whereas it was inhibited by other nucleotides. At low concentrations of CMP, AMP and other nucleotides stimulated inositol incorporation. No such effect was observed when the concentration of CMP was 2 mM or higher. It was found that an appreciable hydrolysis of CMP to cytidine and inorganic phosphate occurred during incubation with microsomes in the presence of Mg2+ or Mn2+. AMP was hydrolysed at a comparable rate. The activatory effect of AMP and other nucleotides on the CMP-dependent incorporation of inositol could be ascribed to protecting CMP against hydrolysis.