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Decrease of platelet intracellular pH and adhesion by ticlopidine in patients with vascular disease
1Institute of Medical Clinics and Chemistry and Clinic Microscopics, University of Verona, Italy.
Insights
Ticlopidine reduces platelet adhesion to fibrinogen but not collagen. This effect is not linked to changes in intracellular calcium, suggesting ticlopidine may inhibit the Na+/H+ antiport.
Area of Science:
- Cardiovascular Research
- Hematology
- Pharmacology
Background:
- Ticlopidine is an antiplatelet medication that inhibits fibrinogen binding to its receptor.
- The study investigates ticlopidine's impact on platelet signal transduction pathways, specifically the Na+/H+ pump and intracellular calcium levels.
Purpose of the Study:
- To determine if ticlopidine's inhibition of platelet aggregation is mediated by alterations in platelet intracellular calcium or Na+/H+ pump activity.
- To assess the effect of ticlopidine on platelet adhesion to various surfaces and its influence on intracellular pH and calcium dynamics.
Main Methods:
- Platelet adhesion, intracellular calcium, and intracellular pH were measured in 13 peripheral vascular disease patients before and after 30 days of ticlopidine treatment (250 mg b.i.d).
- Platelet adhesion was assessed using microplates coated with plasma, fibrinogen, or collagen, with and without ADP stimulation.
- Intracellular calcium and pH changes were measured using fluorescent indicators Fura 2 and BCECF, respectively, following stimulation with ADP and thrombin.
Main Results:
- Ticlopidine significantly reduced platelet adhesion to plasma and fibrinogen by approximately 50% but did not affect adhesion to collagen.
- No significant differences were observed in basal or ADP-induced intracellular calcium levels before and after ticlopidine treatment.
- A significant reduction in basal intracellular pH was noted, along with a decrease in early acidification not dependent on Na+/H+ exchange.
Conclusions:
- The findings do not support the hypothesis that ticlopidine reduces platelet adhesion by altering intracellular calcium signaling pathways.
- The observed reduction in basal intracellular pH and early acidification suggests a potential inhibitory effect of ticlopidine on the Na+/H+ antiport mechanism.
Background:
Ticlopidine inhibits platelet aggregation by preventing the binding of fibrinogen to its platelet receptor. We examined whether this inhibition involved platelet transduction system such as Na+/H+ pump and platelet intracellular calcium.
Methods:
Platelet adhesion in 13 patients with peripheral vascular disease treated with ticlopidine, 250 mg b.i.d for 30 days, was measured in culture microplates before and after therapy. The microplate wells were coated with human plasma, fibrinogen or collagen, and platelet adhesion was studied in the resting condition and after stimulation with 1 and 10 microM ADP. At the same time, platelet intracellular calcium and ADP-induced calcium increases were measured with the fluorescent indicator Fura 2. In addition, intracellular pH and thrombin-induced pH variations were measured with the fluorescent probe BCECF.
Results:
Platelet adhesion to plasma and fibrinogen was significantly reduced (about 50%) after treatment with ticlopidine, while adhesion to collagen was not modified. Basal calcium and ADP-induced calcium increase were not significantly different before and after ticlopidine. Platelet basal intracellular pH was reduced (from 7.44+/-0.009 to 7.41+/-0.017, p<0.05), but agonist-induced alkalinisation was not significantly different. Early acidification, not dependent on Na+/H+ exchange, was also reduced (p<0.05).
Conclusions:
These data do not seem to support the hypothesis that ticlopidine-induced reduction of platelet adhesion depends on alteration of the mechanisms determining signal transduction, at least as far as basal and post-stimulation intracellular calcium is concerned. On the contrary, the possibility that ticlopidine inhibits the Na+/H+ antiport remains open to consideration.