Safety and efficacy of picotamide, a dual anti-thromboxane agent, in patients with thrombocytosis and a previous thromboembolic event: a 1-year observational study

Synthesis and in vitro anti-platelet aggregation activities of 2-methoxy-5-arylamido-N-(pyridin-3-yl-methyl)benzamides

In order to discover novel compounds with anti-platelet aggregation activities, a series of novel 2-methoxy-5-arylamido-N-(pyridin-3-ylmethyl)benzamides (1a-n) were synthesized and their anti-platelet aggregation activities were evaluated by the turbidimetric method in response to the following agonists: adenosine diphosphate (ADP) (5 mM/L), arachidonic acid (AA) (20 µM/L), and collagen (1 mg/mL). Those synthesized compounds that have better in vitro activities were subjected to cell toxicity tests via cell counting kit-8 (CCK-8) assay. The biological evaluation revealed that compound 1a (IC₅₀ : 0.21 µM/L) exhibited the highest anti-platelet aggregation activities when ADP was selected as an inducer, and compound 1b (IC₅₀ : 0.23 µM/L) showed the best activities when AA was selected as inducer, and compound 1m (inhibition rate: 55.06%) had significant anti-platelet aggregation activities when collagen was selected as inducer among all target compounds. Moreover, the effect of cell toxicity exhibited that none of the compounds had obvious cell toxicity against L929 cells. Therefore, 2-methoxy-5-arylamido-N-(pyridin-3-ylmethyl)benzamides have the potential to become a novel kind of anti-platelet drugs and deserve further study.

Inhibitors of platelet signal transduction as anti-aggregatory drugs

In the treatment and prevention of cardiovascular diseases, inhibition of platelet aggregation is of fundamental importance. Inhibition of platelet aggregation can be achieved by either inhibition of membrane receptors or by interception of signalling pathways. While receptor antagonism provides high specificity, the inhibition of platelet signal transduction is more effective. The effectiveness results from the inhibition of platelets, regardless of the cause of activation. These common pathway inhibitors are either intercepting platelet activating mechanisms or amplifying the action of endogenous platelet inhibitors. The physiological anti-aggregants are the endothelial factors NO and prostacyclin, which elevate intracellular cGMP or cAMP content, respectively. By administration of NO-releasing agents, prostacyclin analogues or other cyclic nucleotide elevating drugs the platelet anti-aggregatory action of endothelial factors can be effectively mimicked. Besides antiplatelet activity these drugs also act on vascular smooth muscle causing relaxation and therefore vasodilation, an additional beneficial effect. Inhibition of phosphodiesterases causes elevation of platelet cyclic nucleotide content and thus inhibits platelet aggregation and causes vasodilation. Another relevant target for anti-aggregatory treatment is the arachidonic acid metabolic pathway. This pathway can be intercepted by blockade of either cyclooxygenase-1 (COX-1) or thromboxane synthase. Inhibition of these enzymes may be further amplified by additional antagonism of the thromboxane receptor thus not only preventing formation of thromboxane but also activation of thromboxane receptor by thromboxane precursors, which were particularly effective in clinical trials. In vivo these precursors may be metabolised to prostacyclin in the endothelium and consequently provide additional platelet anti-aggregatory activity. A rather new target for platelet anti-aggregatory treatment is the ecto-nucleotidase CD-39 which limits the plasma level of nucleotides. While several of the novel anti-aggregatory drugs were disappointing in clinical studies combinations of drugs with different effector enzymes showed potent antithrombotic efficacy.

Correlation of Thrombosis With Increased Platelet Turnover in Thrombocytosis

There are no readily applicable methods to routinely assess thrombosis risk and treatment response in thrombocytosis. Reticulated platelets (RP) define the most recently released platelets in the circulation, and the RP% has been shown to estimate platelet turnover in thrombocytopenic states. We examined whether increased RP values were associated with thrombotic complications in thrombocytosis. Platelet count, RP%, and absolute RP count were measured at presentation in 83 patients with chronic or transient thrombocytosis, 46 patients with deep vein (DVT) or arterial (ART) thrombosis and normal platelet counts, and 83 healthy controls with normal platelet counts. Chronic thrombocytosis patients presenting with thrombosis (n = 14) had significantly higher RP% (14.7% ± 10.1%, mean ± SD) than asymptomatic chronic thrombocytosis patients (n = 23, RP% = 3.4% ± 1.8%), healthy controls (3.4% ± 1.3%), DVT patients (n = 21, 3.8% ± 2.1%), or ART patients (n = 25, 4.5% ± 4.1%, P < .05 for all comparisons). Chronic thrombocytosis patients with thrombosis also had significantly higher absolute RP counts than asymptomatic chronic thrombocytosis patients (98 ± 64 × 109/L [range, 54 to 249 × 109/L] v 30 ± 13 × 109/L [range, 11 to 51 × 109/L]; P = .0004), whereas healthy controls, DVT, and ART patients had similarly low absolute RP counts (6 ± 6 × 109/L, 9 ± 7 × 109/L, and 11 ± 7 × 109/L, respectively; P > .49). The RP% and absolute RP counts remained significantly higher in chronic thrombocytosis patients with thrombosis when patients were further subdivided into primary myeloproliferative disorders versus secondary thrombocytosis. Similarly elevated RP percentages and absolute counts were also noted in transient thrombocytosis patients with thrombosis (n = 6, 11.5% ± 4.4% and 90 ± 46 × 109/L, respectively) when compared with asymptomatic transient thrombocytosis patients (n = 40, 4.5% ± 2.7% and 35 ± 16 × 109/L, respectively) and to all control groups (P < .05 for all comparisons). In addition, 7 of 8 thrombocytosis patients who were studied before developing symptoms of thrombosis had elevated absolute RP counts compared with only 1 of 63 thrombocytosis patients who remained asymptomatic. Follow-up studies in seven chronic thrombocytosis patients showed that successful aspirin treatment of symptomatic recurrent thrombosis significantly reduced the RP% from 17.1% ± 10.9% before therapy to 4.8% ± 2.0% after therapy; absolute RP counts decreased from 102 ± 67 × 109/L to 26 ± 10 × 109/L (P < .01 for both). We conclude that thrombosis in the setting of an elevated platelet count is associated with increased platelet turnover, which is reversed by aspirin therapy. Measurement of reticulated platelets to assess platelet turnover may be useful in evaluating both treatment response and thrombotic risk in thrombocytosis.

New antiplatelet drugs

Antiplatelet drugs are used in a wide range of disorders, either as sole agents or as adjuncts to other therapies. Aspirin has been shown to be clinically effective in a number of ischaemic conditions and has been in use for many years. The newer agents, ticlopidine and clopidogrel (which are thought to inhibit ADP-mediated platelet reactions) are also effective and may prove to be superior to aspirin in certain indications. However, ticlopidine in particular has a different spectrum of side-effects, which may eventually limit its widespread use. The Gp IIb/IIIa antagonists have been most extensively investigated in the acute coronary syndromes, and shown to significantly improve outcome. Most of these studies have utilized agents which need to be given parenterally, and subsequently oral compounds are currently being developed. A number of other antiplatelet drugs such as prostacyclin and its analogues, as well as thromboxane inhibitors have been studied over the years, but overall they have failed to demonstrate any real clinical advantage.