Vascular Damage Correlates between Heparin-Induced Thrombocytopenia and the Antiphospholipid Syndrome

Antibody-mediated disorders of heparin-induced thrombocytopenia and antiphospholipid antibody syndrome have remarkably similar clinical presentations, both of which can progressively result in severe vascular and thrombotic disorders. We hypothesized that the mechanism of platelet activation as occurs in heparin-induced thrombocytopenia may also occur in antiphospholipid antibody syndrome particularly at the vascular wall, that endothelial injury may be similar in heparin-induced thrombocytopenia and antiphospholipid antibody syndrome, and that these alterations may be caused by related antibodies. Antibody titers and vascular endothelial damage in patients with heparin-induced thrombocytopenia and antiphospholipid antibody syndrome were studied in plasma samples collected from normals (n = 17), heparin-induced thrombocytopenia patients (n = 15), antiphospholipid antibody syndrome patients (n = 30), and patients clinically diagnosed with antiphospholipid antibody syndrome and heparin-induced thrombocytopenia (n = 8). Diagnosis of heparin-induced thrombocytopenia was confirmed by 14C-serotonin release assay or positive antiheparin-platelet factor 4 antibody titer, and antiphospholipid antibody syndrome was confirmed by positive anti-β2-glycoprotein (GP) 1/cardiolipin (IgG or IgM) antibody titer. The antiheparin-platelet factor 4 antibody was not detected in any patient with antiphospholipid antibody syndrome. Patients with heparin-induced thrombocytopenia did not have elevated IgG anti-β2-GP1 titers, but three (20%) patients had low-positive IgM anti-β2-GP1 titers. The endothelial damage markers of soluble thrombomodulin, soluble P-selectin ( p < 0.05 vs. normal), plasminogen activator inhibitor-1 and tissue factor were elevated in heparin-induced thrombocytopenia and antiphospholipid antibody syndrome patients. The soluble E-selectin was elevated only in the patients with both heparin-induced thrombocytopenia and antiphospholipid antibody syndrome ( p < 0.05 vs. normal). Levels of soluble L-selectin and von Willebrand factor were not different from normals. The pathogenesis of heparin-induced thrombocytopenia and antiphospholipid antibody syndrome appears to be due to two distinct antibodies but associated with similar damage to the vascular endothelium in both diseases.

Syndromes of Thrombosis and Hypercoagulability: Congenital and Acquired Thrombophilias

This article stresses the common hereditary and acquired blood protein defects associated with thrombosis. The most common of the hereditary defects apear to be APC-R, SPS, antithrombin, protein C, and protein S deficiency, and the most common acquired defects are anticardiolipin antibodies and the lupus anticoagulant (antiphospholipid antibodies). Therefore, these are the defects that should first be looked for in an individual with unexplained thrombosis. If these more common defects are not found, then the rarer defects including HC II, plasminogen or TPA deficiency, dysfibrinogenemia, el evated PAI-1 and hyperhomocysteinemia should be sought. The importance of finding these defects has significant impli cations for therapy of the individual patient and for institutions of family studies to identify, inform, and possibly treat others at risk. It is expected that as knowledge of hemostasis expands, more hereditary and acquired defects, such as elevated lipopro tein (a) or defects of extrinsic (tissue factor) pathway inhibitor (EPI, TFPI), may be associated with enhanced risks of throm bosis. Finally, it must be recalled that a diagnosis of thrombo sis, like that of anemia, is only a generic and partial diagnosis; just as in the anemic patient, the etiology must be clearly de fined. Only in this manner can cost-effective and appropriate therapy for both primary treatment and secondary prevention be designed. In addition, the demonstration of a hereditary defect will allow primary prevention in afflicted family mem bers by allowing the choice of appropriate therapy.

Chronic pulmonary hypertension--the monocrotaline model and involvement of the hemostatic system

Monocrotaline (MCT) is a toxic pyrrolizidine alkaloid of plant origin. Administration of small doses of MCT or its active metabolite, monocrotaline pyrrole (MCTP), to rats causes delayed and progressive lung injury characterized by pulmonary vascular remodeling, pulmonary hypertension, and compensatory right heart hypertrophy. The lesions induced by MCT(P) administration in rats are similar to those observed in certain chronic pulmonary vascular diseases of people. This review begins with a synopsis of the hemostatic system, emphasizing the role of endothelium since endothelial cell dysfunction likely underlies the pathogenesis of MCT(P)-induced pneumotoxicity. MCT toxicology is discussed, focusing on morphologic, pulmonary mechanical, hemodynamic, and biochemical and molecular alterations that occur after toxicant exposure. Fibrin and platelet thrombosis of the pulmonary microvasculature occurs after administration of MCT(P) to rats, and several investigators have hypothesized that thrombi contribute to the lung injury and pulmonary hypertension. The evidence for involvement of the various components of the hemostatic system in MCT(P)-induced vascular injury and remodeling is reviewed. Current evidence is consistent with involvement of platelets and an altered fibrinolytic system, yet much remains to be learned about specific events and signals in the vascular pathogenesis.

Syndromes of thrombosis and hypercoagulability. Congenital and acquired causes of thrombosis

Blood coagulation protein and platelet defects are now known to account for up to ninety percent of unexplained venous thrombosis and up to seventy percent of unexplained arterial thrombotic or ischemic events. This article summarizes the common and uncommon blood protein and platelet defects which should be suspected, and searched for, in patients with such events. Defining such defects will have major impact on secondary prevention and duration of antithrombotic therapy in the afflicted patient and impact on primary prevention for identified family members in those harboring hereditary defects.

Hypercoagulability and thrombosis

This article has stressed the common hereditary and acquired blood protein defects associated with thrombosis. The commonest hereditary defects appear to be antithrombin, protein C, and protein S deficiency, and the commonest acquired defects are anticardiolipin antibodies and the lupus anticoagulant. Therefore these are the defects that should first be looked for in an individual with unexplained thrombosis. If these commoner defects are not found, the rarer defects, including HC-II, plasminogen or t-PA deficiency, dysfibrinogenemia, or elevated PAI-1, should next be sought. The incidence of activated protein C cofactor deficiency is not yet clear but may also represent a common defect. Likewise, PAI-1 defects may, with time, be shown to be quite common. The importance of finding these defects has significant implications for therapy of the individual patient and for institution of family studies to identify, inform, and possibly treat others at risk. It is expected that as knowledge of hemostasis expands, more hereditary and acquired defects, such as elevated lipoprotein (a) or defects of extrinsic (tissue factor) pathway inhibitor may be associated with enhanced risks of thrombosis.