thromboxane-a2 and Hemolytic-Uremic-Syndrome

Thrombotic thrombocytopenic purpura is an uncommon, life-threatening disorder that affects older children and adolescents as well as adults. A variety of theories have been proposed to explain its clinical and pathologic manifestations, but the pathophysiology remains poorly understood. It is not even clear whether this disease primarily affects the endothelial cell, the platelet, or both. Most patients have no discernable predisposition to this disease. Our failure to define the pathophysiology of thrombotic thrombocytopenic purpura adequately has hampered our ability to design rational and consistently successful therapy. The present knowledge of this pathophysiology is discussed in detail. The high mortality of this disease necessitates rapid diagnosis so that therapy can be instituted as quickly as possible. The clinical manifestations and diagnostic criteria of thrombotic thrombocytopenic purpura are therefore reviewed.

Topics: Anemia, Hemolytic; Blood Coagulation Factors; Blood Platelets; Child; Diagnosis, Differential; Endothelium; Epoprostenol; Factor VIII; Female; Fever; Fibrinolytic Agents; Hemolytic-Uremic Syndrome; Humans; Kidney Diseases; Male; Neurologic Manifestations; Platelet Activating Factor; Purpura; Purpura, Thrombotic Thrombocytopenic; Thromboxane A2

Topics: Adenosine Diphosphate; Adult; Antigen-Antibody Complex; Arachidonic Acids; Blood Coagulation; Blood Platelets; Blood Vessels; Child; Child, Preschool; Endothelium; Epoprostenol; Hemolytic-Uremic Syndrome; Humans; Kidney; Plasma Exchange; Platelet Adhesiveness; Platelet Aggregation; Purpura, Thrombotic Thrombocytopenic; Thrombin; Thromboxane A2

Previous studies have reported various abnormalities in prostacyclin (PGI2) synthesis and metabolism in hemolytic-uremic syndrome (HUS). However, the conclusions of most of these studies are based on in vitro or ex vivo experiments that only give an indirect estimate of the actual biosynthesis in vivo. We studied the urinary excretion of PGI2 metabolites, taken as a marker of the actual biosynthesis, in six children with HUS during the acute phase of the disease and again when remission was achieved. Eight age- and sex-matched healthy children were studied as controls. Since HUS is also associated with platelet activation and consumption, we also studied the urinary excretion of thromboxane A2 (TxA2) metabolites. Urinary PGI2 and TxA2 metabolites were assessed by radioimmunoassay after high-performance liquid chromatography (HPLC) purification. Urinary excretion of the PGI2 hydrolysis product, 6-keto-PGF1 alpha, was significantly reduced in children with acute HUS as compared with controls, indicating a defective renal synthesis of PGI2. A significant inverse correlation was found between urinary 6-keto-PGF1 alpha and blood urea nitrogen (BUN), as well as plasma creatinine. At remission, urinary 6-keto-PGF1 alpha levels increased to values higher than those of controls. By contrast, the urinary excretion of the major PGI2 beta-oxidation product, 2,3-dinor-6-keto-PGF1 alpha, was comparable to controls, indicating normal systemic PGI2 biosynthesis. The urinary excretion of both TxA2 hydrolysis product, TxB2, and the major beta-oxidation metabolite, 2,3-dinor-TxB2, were lower than normal in the acute phase of HUS if expressed as absolute values.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Child; Child, Preschool; Epoprostenol; Female; Hemolytic-Uremic Syndrome; Humans; Kidney; Linear Models; Male; Platelet Activation; Prostaglandins; Thromboxane A2; Thromboxane B2

Vascular endothelial cell damage plays a central role in the pathogenesis of the hemolytic uremic syndrome (HUS), resulting in intravascular platelet activation and thrombotic microangiopathy. A deficiency of the antiaggregatory prostacyclin (PGI2) has been postulated by experiments under ex vivo conditions. However, this observation has not been confirmed in vivo. The pathophysiological contribution of thromboxane (Tx)A2, a potent vasoconstrictor and platelet-aggregating prostanoid which is predominantly produced by platelets, has not been elucidated so far. In order to quantitate endogenous formation of TxA2 in children with HUS, plasma concentrations of the enzymatic metabolite 11-dehydro-TxB2 of TxA2 and urinary excretion rates of three major TxA2 metabolites, TxB2, 11-dehydro-TxB2 and 2,3-dinor-TxB2 were analyzed using gas chromatography/mass spectrometry. PGI2 biosynthesis was assessed by measuring urinary excretion of an index metabolite of its systemic production, 2,3-dinor-6-keto-prostaglandin (PG) F1 alpha, and an index of its renal production, 6-keto-PGF1 alpha. TxA2 biosynthesis was markedly elevated in the acute phase of HUS. This activation could be detected for a longer period of time than the presence of thrombocytopenia. Concomitantly in the acute phase, renal PGI2 formation was significantly elevated and systemic PGI2 formation was elevated in 50% of the patients. These data indicate that TxA2 formation is increased in the acute phase in patients with HUS. This enhanced biosynthesis is consistent with increased platelet activation, whereas the increased PGI2 biosynthesis reflects predominantly renal endothelial cell damage.

Topics: Child; Child, Preschool; Creatinine; Epoprostenol; Female; Hemolytic-Uremic Syndrome; Humans; Infant; Male; Platelet Activation; Prostaglandins; Thromboxane A2; Thromboxane B2

Prostacyclin is a very unstable prostaglandin, which is continuously synthetized and released by blood vessels. It fulfills 2 main functions, namely strong inhibition of platelet aggregation and vasodilation. Thus it acts as an important defense mechanism of the vascular wall, which is directed against overwhelming platelet aggregation and against the development of atherosclerosis. Besides endogenous prostacyclin is an important antihypertensive factor. In several diseases, as diabetes mellitus, obliterative arteriopathy and haemolytic-uraemic syndrome, the reduced prostacyclin-synthesis is thought to be a key mechanism for the development of vascular lesions. On the other hand the haemorrhagic diathesis of uraemics is seen in connection with an increased vascular prostacyclin release. Synthetic prostacyclin is now under trial for therapy in peripheral obliterative arteriopathy and extracorporeal circulation, as haemodialysis and cardiopulmonary bypass.

Topics: Arteriosclerosis; Diabetic Angiopathies; Epoprostenol; Female; Hemolytic-Uremic Syndrome; Humans; Intermittent Claudication; Muscle, Smooth, Vascular; Platelet Aggregation; Pre-Eclampsia; Pregnancy; Prostaglandins; Purpura, Thrombotic Thrombocytopenic; Thromboxane A2; Vasodilation