thromboxane-b2 and Thalassemia

Aspirin is now recommended for splenectomized thalassemia patients with high platelet counts. However, aspirin resistance defined by arachinodic acid (ACA) induced platelet aggregation ≥20%, has never been reported in this group of patients. In this study, twenty-four splenectomized thalassemia patients (15.7±4.1years), with platelet counts ≥800x10(9)/L, and 21 non-splenectomized severe thalassemia patients (14.3±3.2years), were enrolled. After taking aspirin (2mg/kg/day), seven patients (29.2%) displayed aspirin resistance. Serum thromboxane B2 (TXB2) levels in the aspirin responsive group decreased significantly [52.6(8.8-174.6) vs 4.0(1.6-7.3) mcg/mL, p<0.001], while no change was demonstrated in the aspirin resistant group. Having increased aspirin to 4mg/kg/day, three of the seven aspirin resistant patients responded, while one developed upper GI bleeding from esophageal varices and was withdrawn from the study. For the three remaining patients, their doses were increased to the maximum of 300mg/day, and two of the three responded. Thrombin antithrombin complex and D-dimer levels were significantly decreased after taking aspirin (2mg/kg/day), although D-dimer level was still significantly higher than that in non-splenectomized group. Therefore, aspirin dosage can be adjusted individually to reach maximum effect of platelet inhibition. In addition, aspirin can reduce the levels of coagulation markers.

Topics: Adolescent; Aspirin; Blood Coagulation; Child; Child, Preschool; Drug Resistance; Female; Fibrin Fibrinogen Degradation Products; Humans; Male; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Count; Platelet Function Tests; Splenectomy; Thalassemia; Thromboembolism; Thromboxane B2; Young Adult

Increased frequency of thromboembolic events has been recently observed in patients with beta-thalassemia major (TM). Platelet function anomalies including impaired aggregation, increased circulating aggregates, and our finding of shortened platelet survival indicate that platelets may be involved in the hypercoagulability in thalassemia. Consequently, we used a technique based on thin layer chromatography purification and enzyme immunoassay to measure urinary metabolites of thromboxane A2 (TXA2) and prostacyclin (PGI2) in nine splenectomized patients with beta-TM regularly transfused, five non-splenectomized patients with beta-thalassemia intermedia (TI), and 20 healthy individuals. A significant 4- to 10-fold increase was observed in the urinary excretion of 2,3-dinor-TXB2, 11-dehydro-TXB2 and 2,3-dinor-6-keto-PGF1 alpha in patients with TM and TI as compared with healthy controls. No significant differences were found in the concentrations of these metabolites between TM and TI patients. Six TM patients received a very low dose of aspirin (20 mg/day) for 7 days. A significant decrease was observed in the urinary concentrations of 2,3-dinor-TXB2 and 11-dehydro-TXB2 derived from platelets. However, the levels of urinary 2,3-dinor-6-keto-PGF1 alpha reflecting vascular production and TXB2 and 6-keto-PGF1 alpha originating from the kidney were not significantly changed. These results are consistent with those of increased in vivo production of TXA2 because of endogenous platelet activation.

Topics: 6-Ketoprostaglandin F1 alpha; Adolescent; Adult; Aspirin; Female; Humans; Male; Platelet Activation; Thalassemia; Thromboxane B2