Interaction of ticlopidine with the erythrocyte membrane

Red cell filterability and erythrocyte membrane microviscosity during ticlopidine treatment

The effects of 10 days' treatment with 500 mg/day ticlopidine on the filterability of red blood cells in suspension and on the microviscosity of the red blood cell membrane was evaluated in 11 patients with vascular atherosclerosis. The results show ticlopidine to be effective in influencing the rheological measures of red cell filterability and membrane microviscosity: filterability was increased and microviscosity was decreased. Ticlopidine also decreased the extent of fluorescence polarization. These results are discussed regarding possible mechanisms of action of ticlopidine.

Glucose and erythrocyte ATP: distinctive effects of dipyridamole and of ticlopidine

This experiment suggests the following points: 1. Erythrocytes in control patients and in atherosclerosis patients seem to have a variable grade of affinity for adenosine and for plasma glucose. This variable grade seems to fix the level of the adenosine triphosphate (ATP) reserves and induces the erythrocytes' deformability. 2. The drop in the level of ATP reserves that induces the poor deformability of the erythrocytes in atherosclerosis patients would appear to be caused by two consecutive shortages: first a shortage that seems to be related to a deficiency of erythrocyte adenosine as the ATP shortage disappears with dipyridamole treatment and then a shortage induced by the lack of erythrocyte glucose and suppressed by the addition of ticlopidine to the dipyridamole treatment.

Swelling of mitochondria by the platelet antiaggregating agent ticlopidine

Our studies on the effects of ticlopidine on mitochondrial functions led us to an intriguing observation related to its interaction with mitochondrial membranes. Liver mitochondria were isolated from Sprague-Dawley rats and assayed for swelling by spectrophotometry. When ticlopidine was added to mitochondria preincubated in an isotonic test medium, an induced-swelling activity was observed. This activity was time and concentration dependent and occurred in different isosmotic solutions. Several analogues of ticlopidine, assayed under identical conditions, produced only a minor effect. Respiratory chain inhibitors, uncouplers, ATP, and phosphate protected the mitochondria against the ticlopidine-induced swelling, whereas oligomycin did not. Comparative studies with the drugs chloramphenicol, nitroso-chloramphenicol, and salicylate (known for their association with mitochondrial injury) showed the first two to have little effect while the third one caused swelling as expected. On the other hand, oxypolarographic tests of respiring mitochondria in the presence of ticlopidine showed that the drug is not an uncoupling agent. These results indicate that the antiaggregating agent ticlopidine interacts with mitochondrial membranes causing swelling which, in turn, may alter mitochondrial permeability; however, unlike some other swelling agents, it does not act as a classical uncoupler.

Spin label study of the effect of ticlopidine on platelets

The effect of ticlopidine on platelet membrane fluidity was investigated using a spin label technique. Ticlopidine, when orally administered to rats, increased both the order parameter and the motion parameter, indicating a decrease in the membrane fluidity of platelets. On the other hand, the order parameter and the motion parameter decreased markedly when the platelets were aggregated by thrombin. Ticlopidine inhibited the thrombin-induced aggregation of platelets and caused a slight increase in order parameter and motion parameter in thrombin-aggregated platelets. Judging from sodium dodecyl sulfate polyacrylamide gel electrophoresis, ticlopidine did not modify the electrophoretic pattern of platelet proteins appreciably. Ticlopidine decreased cholesterol/phospholipids molar ratio and increased slightly total amounts of proteins of the platelets. These results indicate that the inhibitory action by ticlopidine was accompanied by changes in membrane fluidity, and these changes were due to a perturbation of the membrane phospholipid core of the platelets by ticlopidine and/or its metabolites.

Interaction of vinblastine sulfate with artificial phospholipid membranes. A study by differential scanning calorimetry and spin labeling

The effect of the antimitotic drug vinblastine sulfate has been studied on fully hydrated dipalmitoylphosphatidylcholine (DPPC) liposomes in the temperature range 0 degrees to 60 degrees using differential scanning calorimetry and electron spin resonance spectroscopy with two fatty acid spin labels. In the gel phase, vinblastine interacts essentially with the DPPC polar heads and induces an important disorganization of the phospholipidic bilayer. The co-operativity of the main thermal transition is decreased. In the crystal-liquid phase, the drug penetrates inside the artificial membrane and induces the formation of domains which increased thermal stability. These effects are opposite to those observed with the drug isaxonine which is used to reduce the axonal degenerating effects due to vinblastine.

Membrane expansion as a mechanism explaining the antisickling action of ticlopidine observed in vitro

Ticlopidine, a platelet antiaggregant, has shown some efficacity in a clinical trial in patients with sickle cell disease. We have studied this agent in vitro to evaluate its effects on sickle erythrocyte. Ticlopidine effects sickling in vitro not by direct interaction with hemoglobin, but via strong binding to the red cell membrane. The density of the whole cell population is decreased when cells are treated with 0.1 mM ticlopidine, which is higher than the concentrations of 1 microM potentially achievable in vivo. Since hemoglobin concentration influences the delay time for gelling, its decrease in the red cell could have a beneficial effect. Such a partial inhibition of the polymerization is shown by oxygen equilibrium studies at various ionic strengths.

Effects of ticlopidine, a new platelet antiaggregating agent, and its analogues on mitochondrial metabolism. Oxidative phosphorylation, protein synthesis and DNA polymerase activity

The effects of ticlopidine and six of its analogues on mitochondrial functions were studied in isolated rat liver mitochondria. The influence of ticlopidine and each of the following analogues: PCR 5325, PCR 4099, PCR 3787, PCR 2362, PCR 4499 and PCR 0665 was evaluated by determining their interaction with three major mitochondrial activities. (A) Oxidative phosphorylation, measured by oxypolarography, was assayed in the presence of glutamate or succinate as source of energy, and both State 4 and State 3 were recorded. Ticlopidine, at 20 micrograms/ml, slightly increased glutamate State 4, whereas it was without effect on that of succinate. At higher concentration (40 micrograms/ml), ticlopidine caused 40-45% inhibition of State 4 with both substrates. All the other analogues tested at either 20 or 40 micrograms/ml were virtually without effect on the respiration. However, at 20 micrograms/ml, ticlopidine and some of its analogues inhibited mitochondrial State 3, while under similar conditions other analogues had little or no effect on this state. (B) Mitochondrial protein synthesis, measured by [14C]-L-leucine incorporation, was not affected significantly by any of these drugs. Whereas chloramphenicol at 10 micrograms/ml caused 80% inhibition, ticlopidine and its analogues in concentrations inhibitory to State 3 did not inhibit mitochondrial protein synthesis. (C) Mitochondrial DNA polymerase activity, determined by [3H] thymidine 5'-triphosphate incorporation, was not inhibited by these drugs. We conclude that, while ticlopidine and analogues have little or no effect on either mitochondrial protein synthesis or mitochondrial DNA polymerase activity, ticlopidine and some of its analogues are inhibitory of the energy conserving mechanism in mitochondria.

Isaxonine base is a strong perturber of phospholipid bilayer order and fluidity--a differential scanning calorimetry and spin labeling study

The effects of the neurotropic drug isaxonine on fully hydrated dipalmitoyl-phosphatidyl-choline (DPPC) bilayers has been studied in the temperature range 0 degree-60 degrees, using differential scanning calorimetry and electron spin resonance spectroscopy, with two stearic acid spin labels. At low concentration (1% mol/mol), isaxonine is trapped in the polar interface and enhances the phospholipid multibilayers organization in the gel state. In contrast, at high concentration (30% mol/mol), the drug disorganizes the phospholipidic structures and may induce domain formation by phase separation. The strong interactions of isaxonine at the lipid-water interface change the ionization state of the stearic acid spin labels which become totally ionized. Then isaxonine acts as a modifier of the surface pH of the bilayer. The strong membrane effects of isaxonine may explain in part its pharmacological properties in vivo.