thromboxane-b2 and Anemia--Sickle-Cell

Pregnancy increases the risk of morbidity and mortality in sickle cell disease. We previously showed pregnant women with sickle cell disease to have a relatively low plasma renin concentration in late pregnancy, associated with a lack of the expected plasma volume expansion. We hypothesized this to be due to increased systemic vascular resistance through an imbalance between the vasodilator prostacyclin and vasoconstrictor thromboxane, associated with decreased glomerular filtration rate (GFR).. To compare estimated prostacyclin, thromboxane and GFR in non-pregnant and pregnant women with hemoglobin SS (HbSS) and AA (HbAA).. Four groups of 20 normotensive, nulliparous women were studied in Lagos, Nigeria: pregnant HbSS or HbAA women at 36-40 weeks gestation; non-pregnant HbSS and HbAA controls. We measured stable metabolites of prostacyclin and thromboxane A2 by enzyme-linked immunosorbent assay; GFR using the Cockcroft-Gault equation. Data analysis was by independent (Student's) t-test or Mann-Whitney U test for comparisons between any two groups of continuous variables, univariate ANOVA for multiple groups and Pearson's correlation coefficient for degree of association between variables.. HbSS women had lower serum 6-keto-PGF1α concentrations than HbAA, whether pregnant or non-pregnant (P<0.001; P<0.004 respectively). Conversely, pregnant HbSS women had higher serum TxB2 (P<0.001); non-pregnant HbSS women had non-significantly higher TxB2 concentrations. The 6-keto-PGF1α:TxB2 ratio was markedly increased (pro-vasodilatory) in HbAA pregnancy (P<0.001) but reduced in HbSS pregnancy (P = 0.037). GFRs (mL/min) were higher in non-pregnant HbSS than HbAA (P<0.008) but only marginally raised in HbSS women in late pregnancy (P = 0.019) while markedly raised in HbAA pregnancy (P<0.001).. The lower ratio of prostacyclin-thromboxane metabolites in HbSS pregnancy may indicate endothelial damage and an increased tendency to vasoconstriction and clotting. If confirmed by subsequent longitudinal studies, interventions to increase prostacyclin and reduce thromboxane, such as low dose aspirin, may be potentially useful in their management.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Anemia, Sickle Cell; Blood Pressure; Creatinine; Cross-Sectional Studies; Eicosanoids; Epoprostenol; Female; Genotype; Glomerular Filtration Rate; Humans; Longitudinal Studies; Pregnancy; Pregnancy Outcome; Thromboxane A2; Thromboxane B2; Thromboxanes; Young Adult

Plasma levels of 6-keto-prostaglandin F1 alpha (6kPGF1 alpha) and thromboxane (Tx) B2 have been assessed in sickle cell disease (SCD) with discrepant results. Inasmuch as direct measurement of plasma prostanoids is fraught with the problem of interfering substances, we assessed plasma 6kPGF1 alpha and TxB2 levels in patients with SCD by RIA after extraction of eicosanoids and separation by HPLC. We demonstrate that the 6kPGF1 alpha and TxB2 levels in children with SCD in steady state as well as in vaso-occlusive crisis (VOC) are significantly lower when compared with those from age-matched controls. The VOC plasma 6kPGF1 alpha and TxB2 levels were, however, significantly elevated when compared with those from children in steady state. Changes similar to those noted with unpaired plasma samples were also observed when paired steady state and VOC plasmas from the same patients were assessed. The ratio of TxB2 to 6kPGF1 alpha was, however, significantly elevated in patients with SCD in crisis when compared with eicosanoid ratios obtained during steady state. In an attempt to understand whether the abnormality in 6kPGF1 alpha was due to an impairment in endothelial cell prostacyclin-regenerating ability, we compared the ability of plasma from controls and children with SCD to activate arachidonic acid (AA) release and prostacyclin production by [14C]AA-prelabeled bovine aortic endothelial cells. Our results suggest that the decreased 6kPGF1 alpha levels in plasma from children with SCD was not due to an effect on substrate AA release but rather a modulatory effect of sickle plasma components on endothelial cell cyclooxygenase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Ketoprostaglandin F1 alpha; Adolescent; Adult; Anemia, Sickle Cell; Animals; Arachidonic Acid; Case-Control Studies; Cattle; Cells, Cultured; Child; Child, Preschool; Chromatography, High Pressure Liquid; Constriction, Pathologic; Endothelium, Vascular; Epoprostenol; Humans; Thromboxane B2; Vascular Diseases; Vasoconstrictor Agents; Vasodilator Agents

There is evidence for increased factor VII turnover and the associated increased thrombin generation and fibrinolytic activities in sickle cell disease (SCD) that may affect in vivo platelet and endothelial cell reactivity. We studied the release of specific eicosanoids that are indicative of in vivo platelet activation and endothelial cell injury. The circulating and urinary levels of 2,3-dinor thromboxane B2(2,3-dinor-TxB2),TxB2,PGI2 [as 6-keto-PGF1 alpha], and PGE2 were measured in 15HbSS patients, eight HbAA non-haemolytic anaemic individuals and 12 healthy HbAA controls using specific RIAs. The mean urinary 2,3-dinor-TxB2 in the HbSS patients was significantly higher than in both the healthy HbAA and the anaemic controls. 6-keto-PGF1 alpha was undetected in the urines of the healthy HbAA controls, but was measured insignificant amounts in the HbSS and the HbAA anaemic patients. The urinary concentrations of PGE2 and TxB2 in HbSS patients' samples were also significantly higher than those of both control groups (P < 0.05). PGE2 and TxB2 levels were below the detection limit in the plasmas of the HbAA subjects, but were measurable in the HbSS and HbAA anaemic plasmas. The plasma level of 6-keto-PGF1 alpha in the HbSS patients was also significantly higher than in the control groups. The data indicates a persistent inflammatory process in the HbSS patients, and is consistent with the hypothesis that there is platelet and endothelial cell activation in SCD.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Anemia, Sickle Cell; Blood Platelets; Dinoprostone; Endothelium, Vascular; Humans; Middle Aged; Thromboxane B2

Thrombosis represents an important cause of mortality in patients with sickle cell disease, in addition to the complications caused by the primary defect of inherited abnormal hemoglobin. To study the involvement of platelets in these complications, we assessed the biosynthesis of thromboxane A2 in samples from 49 patients with sickle cell disease and in 33 control subjects. The urinary excretion of the major arachidonic acid metabolite of platelet origin (11-dehydro-thromboxane B2) and of the vascular endothelial cell (2,3-dinor-6-ketoprostaglandin F1 alpha) were very significantly increased (p < 0.0002) in the patients. In a small group of patients (n = 14), we further investigated the ex vivo response of their platelets to U46619, a stable analogue of thromboxane A2. We observed decreased aggregation and [14C]serotonin release compared with control (p < 0.05); similarly, we found impaired p47 protein phosphorylation (p < 0.05). In contrast, platelets from these patients responded normally to thrombin (0.1 unit/mL). In vivo desensitization of platelets from these patients to thromboxane may constitute a form of regulation that may prevent the propagation of aggregation by this potent inducer, as has been hypothesized in in vitro studies. Our results may also provide a rationale for using antiplatelet drugs in the prophylaxis of thrombotic complications in sickle cell patients.

Topics: 6-Ketoprostaglandin F1 alpha; Adolescent; Adult; Anemia, Sickle Cell; Aspirin; Blood Platelets; Female; Humans; Male; Phosphorylation; Prostaglandin Endoperoxides, Synthetic; Thrombin; Thromboxane A2; Thromboxane B2

The increased adhesiveness of sickle erythrocytes (SS RBC) to endothelial cells has been confirmed in a static system utilizing fresh umbilical vein endothelium. Adherence of SS RBC to the endothelium was as great in the presence of calcium-containing buffer as when incubated in plasma. SS RBC suspended in autologous platelet-rich plasma adhered to a greater extent than when suspended in autologous platelet poor plasma. Prostacyclin, thromboxane B2, and an inhibitor of collagen- and epinephrine-induced platelet aggregation (B13.177) did not affect SS RBC adherence to endothelium. Aspirin in a concentration of 5 micrograms/ml slightly decreased SS RBC adherence to endothelium in the presence of platelets. Platelets may play a significant role in the increased adhesiveness of SS RBC to endothelium. To the extent that increased SS RBC adhesiveness contributes to the genesis of painful crises and to the extent platelets augment this adhesiveness, agents affecting platelet function may prove useful in preventing painful crises.

Topics: Anemia, Sickle Cell; Aspirin; Blood Platelets; Cell Adhesion; Endothelium, Vascular; Epoprostenol; Erythrocyte Aggregation; Erythrocytes; Erythrocytes, Abnormal; Hemoglobin, Sickle; Humans; Thromboxane B2

Endothelial cell damage is considered to be the initial step in the genesis of thrombosis and atherosclerosis. Recently, the adhesion of erythrocytes from patients with diabetes or sickle cell anemia to endothelial cells was found to be increased and correlated with the severity of vascular complications. We have measured by radioimmunoassay the release of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) as an index of prostacyclin (PGI2) production, during red cell adhesion to endothelial cells in culture. The amount of 6-keto-PGF1 alpha released after incubation with normal red cells was similar to that observed with buffer (1.07 +/- 0.32 nmol/10(6) endothelial cells). However, after the adhesion of erythrocytes from patients with diabetes or sickle cell anemia, the amount of 6-keto-PGF1 alpha produced was significantly increased (P less than 0.01) and was correlated with the extent of erythrocyte adhesion (P less than 0.05). Tritium-labeled PGI2 was found to bind to erythrocytes, and the binding was time and concentration dependent. PGI2 release was inhibited by the cyclooxygenase inhibitor (flurbiprofen), whereas red cell adhesion remained unchanged. Fibrinogen potentiated erythrocyte adhesion and PGI2 production. The increase in PGI2 production after the adhesion of red cells from patients with diabetes or sickle cell anemia to endothelial cells indicates that endothelium may be damaged by abnormal erythrocyte adhesion.

Topics: 6-Ketoprostaglandin F1 alpha; Adenosine Diphosphate; Adenosine Triphosphate; Adult; Anemia, Sickle Cell; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Blood Proteins; Blood Vessels; Cell Adhesion; Cells, Cultured; Cyclooxygenase Inhibitors; Diabetes Mellitus; Endothelium; Epoprostenol; Erythrocytes; Fibrinogen; Flurbiprofen; Humans; Leukocytes; Middle Aged; Plasma; Prostaglandins F; Thromboxane B2

Platelet and vascular endothelial prostaglandin derivatives were measured by radioimmunoassay in the plasma of 39 children with homozygous sickle cell anaemia and 27 control subjects. The levels of both thromboxane B2 and 6-keto-PGF1alpha, the stable end-products of platelet and vascular prostaglandin metabolism, were significantly (p less than 0.001) greater in sickle cell anaemia plasma than in the plasma of the controls. There were no differences in levels of either 6-keto-PGF1alpha or thromboxane B2 between steady state and vaso-occlusive crisis in the sickle cell patients. Injury to the endothelial lining of blood vessels may occur in sickle cell anaemia as a consequence of contact with the abnormal erythrocytes.

Topics: Adolescent; Adult; Anemia, Sickle Cell; Blood Platelets; Child; Child, Preschool; Humans; Plasma; Prostaglandins; Prostaglandins F; Thromboxane B2

Previous reports have given conflicting conclusions of the role platelets may play in initiating vaso-occlusive sickle cell crisis. Seven patients homozygous for sickle cell hemoglobin, and seven age, race and sex matched controls were each studied on at least two occasions in a six week period of normal health. The number of platelets circulating as aggregates, the plasma concentration of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF-4) were significantly elevated compared with controls. These findings were confirmed with a second series of fourteen patients and nine controls. Patient's platelets in plasma adjusted for both platelet number and citrate concentration aggregated more in response to low concentrations (0.4 and 1 microM) but less to higher concentrations (4 and 20 microM) of ADP and needed significantly more prostacyclin (PGI2) to inhibit ADP induced aggregation than did platelets from control subjects. There was no significant difference in plasma concentration of fibrinopeptide A and thromboxane (Tx)B2, nor in the platelet generation of TxB2 and release of serotonin and beta TG induced by aggregating agents. Thus, the platelets of patients with sickle cell anemia in the steady state are readily activated and respond in vivo by increased formation of aggregates and release of beta TG and PF-4.

Topics: Adenosine Diphosphate; Adolescent; Adult; Anemia, Sickle Cell; beta-Thromboglobulin; Blood Platelets; Epoprostenol; Female; Fibrinopeptide A; Hematocrit; Humans; Male; Platelet Aggregation; Platelet Count; Platelet Factor 4; Thromboxane B2