Cationic amphiphilic drugs as a potential tool for modifying phospholipids of tumor cells. An in vitro study of chlorpromazine effects on Krebs II ascites cells

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.

Changes in cell surface anionogenic groups induced by propranolol in Herpetomonas muscarum muscarum

The effects of propranolol (10(-3) mM) on the surface anionic groups of Herpetomonas muscarum muscarum were analysed by cell electrophoresis, by ultrastructural cytochemistry and by identification of sialic acids using paper chromatography. Differentiation of H. muscarum muscarum induced by propranolol treatment caused a significant increase in the net negative surface charge. Binding of cationized ferritin (CF) and colloidal iron hydroxide particles was observed at the cell surface of both untreated and propranolol-treated cells. In cells incubated in the presence of the drug the CF particles were distributed in all membrane regions. However, there were small areas where the particles were absent. In H. muscarum muscarum exposed to propranolol the density of residues of sialic acid per cell was higher, and the agglutinating activity with Sendai virus was more intense. However, the pattern of sialic acid, characterized by the presence of N-acetylneuraminic acid derivative, was not modified upon cell interaction with the drug. Treatment of both control and propranolol-treated protozoa with neuraminidase significantly reduced the surface charge. These findings suggest that sialic acid residues are the major anionogenic groups exposed on the surface of H. muscarum muscarum.

Action of hemicholinium-3 on phospholipid metabolism in Krebs II ascites cells

Incorporation of [Me-14C]choline or/and [2-14C]ethanolamine into phospholipids of Krebs II ascites cells in toto have been tested in the presence of hemicholinium-3. With [Me-14C]choline, labelling of cell pellet, intracellular choline, phosphocholine and total lipid extract is inhibited by hemicholinium-3 in a dose-dependent way between 6.25 X 10(-6) M and 10(-3) M. These effects are caused by a diminution of the choline or/and ethanolamine transport across the cell membrane and by a choline-kinase inhibition. In Krebs cells, choline is taken up by a low affinity Na+ sensitive uptake system (KT = 46 X 10(-6) M) which is competitively inhibited by hemicholinium-3 (KTi = 161 X 10(-6) M). Krebs cells exert a counter-transport (i.e. an exchange of choline across the membrane) against a concentration gradient of 10 mM choline whereas 10 mM hemicholinium-3 has no effect. Choline-kinase is also inhibited (I50 = 57 X 10(-6) M) in Krebs cells in toto and time-course data suggest that choline transport and phosphorylation might be tightly coupled. Specific radioactivities of phosphocholine and choline-glycerophospholipids decrease owing to the effect of the drug on the uptake and phosphorylation system. With 4 X 10(-5) M hemicholinium-3 and [Me-14C]choline as a marker, labelled choline-glycerophospholipids are decreased by 22%. With [2-14C]ethanolamine, labelled ethanolamine-phospholipids are decreased by 26% and choline-glycerophospholipids remain unlabelled. With the two markers, the additional effect produces a 35% decrease. It is concluded that hemicholinium-3 might be able to induce a depression of the intracellular choline and phosphocholine pool which could provoke a serious quantitative deficiency of major phospholipids in Krebs cells.

Turnover of phosphocholine and phosphoethanolamine in ether-phospholipids of Krebs II ascite cells

Krebs II ascite cells suspended in Eagle medium were incubated at 37 C for up to 6 hr in the presence of [3H] glycerol or [32P] orthophosphate. After extraction, their lipids were treated with guinea pig phospholipase A1 under conditions where all diacyl-phospholipids (diacyl-PL) became hydrolyzed with 55% recovery of lyso-PL. Using a bidimensional thin layer chromatography (TLC) involving exposure to HCl fumes between the two runs, it then became possible to determine at once the specific radioactivity of the three subclasses (diacyl-, alkylacyl- and alkenylacyl-) present in choline glycerophospholipids (CGP) and ethanolamineglycerophospholipids (EGP). Compared to diacyl-PL, a lower de novo synthesis of ether subclasses was evidenced in both CGP and EGP by [3H] glycerol incorporation. Although the same profile was obtained for CGP with [32P] orthophosphate, the three EGP subclasses displayed in this case the same specific radioactivity. These data indicate a higher turnover rate of the polar head group of ether-EGP compared to either-CGP. The simple methodology used in the present study might thus prove helpful in developing enzymatic studies dealing with the mechanism of this accelerated renewal.

Carrier-mediated choline uptake by Krebs II ascites cells

Krebs II ascites cells have a low affinity uptake system for choline (Km = 36 microM, Vm = 76 nmol/min per 2 X 10(8). Choline entered the cells and was rapidly phosphorylated (95% of total intracellular soluble label). Trans acceleration of labeled choline from cells preloaded with radiolabeled choline and postincubated in the presence of unlabeled choline indicates that choline transport in Krebs II ascites cell is carrier mediated. Ethanolamine competed for the choline carrier. The uptake was reduced by hemicholinium-3, iodoacetamide and ouabain. The mechanism of choline transport in Krebs II ascites cells is in agreement with a linear transport model.

An in vitro study of hemicholinium-3 on phospholipid metabolism of Krebs II ascites cells

With [Me-14C]choline as marker and after separation of choline and phosphocholine by ion-exchange column chromatography or thin layer chromatography on alumina, it is shown that 40 microM hemicholinium-3 (HC-3) inhibits the cytosolic choline-kinase of rat liver and Krebs cells. This inhibition is competitive (Km different, Vm similar) in the first case and mixed in the second (Km and Vm different). Despite this general inhibition of the phosphocholine formation, the synthesis of phosphatidylcholine (PC) by post-nuclear supernatants of rat liver and Krebs cells is different when tested with HC-3. It is unaffected in rat liver; however, HC-3 induces a PC deficiency in Krebs cells which is time-course dependent between 15 and 120 min and proportional to the drug concentrations in the interval 5-40 microM. Incorporation of AT-[gamma 32P] or [2-14C]ethanolamine into phospholipids shows that the sequential methylation pathway is not detectable in Krebs cells. These results are discussed in relation to those established concerning HC-3 action on phospholipid metabolism in other tissues.

Effect of chlorpromazine on rat arterial lipid synthesis, in vitro

The effect of chlorpromazine, a major tranquilizer, on arterial lipid metabolism was studied in vitro in rat aortas incubated with [14C]acetate and [14C]mevalonate as lipid precursors. Chlorpromazine at a level of 0.25 mM in the incubation medium significantly reduced the incorporation of [14C]acetate into free fatty acids (p less than 0.01) and total phospholipids (p less than 0.001) but not triglycerides. Chlorpromazine also altered the pattern of arterial phospholipids synthesized from [14C]acetate by significantly increasing the relative proportion of phosphatidylinositol plus phosphatidylserine (p less than 0.02) and reducing the relative proportion of sphingomyelin (p less than 0.001). [14C] Acetate incorporation into the combined fractions of steryl esters plus hydrocarbons and sterols plus diglycerides was also significantly reduced (p less than 0.001) by 0.25 mM chlorpromazine. Studies with [14C]mevalonate showed that chlorpromazine is also an inhibitor of sterol biosynthesis in arterial tissues as evidenced by 35-40% reductions (p less than 0.05) in the formation of 14C-labeled squalene and C27 sterols.