Thrombopoietin primes human platelet aggregation induced by shear stress and by multiple agonists

Recombinant thrombopoietin has been reported to stimulate megakaryocytopoiesis and thrombopoiesis and it may be quite useful to treat patients with low platelet counts after chemotherapy. As little is known regarding the possible activation of platelets by thrombopoietin, we examined the effects of thrombopoietin on platelet aggregation induced by shear stress and various agonists in native plasma. Using hirudin as an anticoagulant, thrombopoietin (1 to 100 ng/mL) enhanced platelet aggregation induced by 2 micromol/L adenosine- diphosphate (ADP) in a dose dependent fashion. The enhancement was not affected by treatment of platelets with 1 mmol/L aspirin plus SQ-29548 (a thromboxane antagonist, 1 micromol/L) but was inhibited by a soluble form of the thrombopoietin receptor, suggesting that the enhancement was mediated by the specific receptors and does not require thromboxane production. Epinephrine (1 micromol/L), which does not induce platelet aggregation in hirudin platelet rich plasma (PRP), did so in the presence of thrombopoietin (10 ng/mL). Thrombopoietin (10 ng/mL) also enhanced or primed platelet aggregation induced by collagen (0.5 micron.mL),. thrombin, serotonin, and vasopressin. Thrombopoietin does not induce any rise in cytosolic ionized calcium concentration nor activation of protein kinase C, as estimated by phosphorylation of preckstrin, indicating that the priming effects of thrombopoietin does not require those processes. The ADP- or thrombin-induced rise in cytosolic ionized calcium concentration was not enhanced by thrombopoietin (100 ng/mL). Further, shear (ca. 90 dyn/cm2)-induced platelet aggregation was also potentiated by thrombopoietin. The priming effect on epinephrine-induced platelet aggregation in hirudin PRP was unique to thrombopoietin, with no effects seen using interleukin-6 (IL-6), IL-11, IL-3, erythropoietin, granulocyte-colony stimulating factor, granulocyte macrophage-colony stimulating factor, or c-kit ligand. These data indicate that monitoring of platelet functions may be necessary in the clinical trials of thrombopoietin.     

Inhibition of endotoxin-induced activation of the coagulation and fibrinolytic pathways using a recombinant endotoxin-binding protein (rBPI23)

A recombinant endotoxin-neutralizing protein, rBPI23, was shown to partially prevent endotoxin-induced activation of the fibrinolytic and coagulation systems in experimental endotoxemia in humans. In a placebo- controlled, blinded crossover study, eight volunteers were challenged twice with an intravenous bolus injection of endotoxin (40 EU/kg of body weight) and concurrently received either rBPI23 (1 mg/kg) or placebo (human serum albumin, 0.2 mg/kg). rBPI23 treatment significantly lowered the endotoxin-induced fibrinolytic response, ie, reduced the release of tissue-type plasminogen activator, urokinase- type plasminogen activator, plasminogen activator inhibitor antigen, and complex formation of plasmin alpha 2-antiplasmin (P = .0078 for each). Plasminogen activator inhibitor activity was also reduced, but not significantly according to the Hochberg method (P = .0304). The endotoxin-induced activation of the procoagulant state as reflected by increase in F1 + 2 fragments and TAT complexes was blunted by rBPI23 infusion (P = .0391 [not significant according to the Hochberg method] and .0078, respectively). These results indicate that rBPI23 is capable of reducing both the activation of the fibrinolytic and the coagulation systems after low-dose endotoxin infusion in humans.     

Crkl is constitutively tyrosine phosphorylated in platelets from chronic myelogenous leukemia patients and inducibly phosphorylated in normal platelets stimulated by thrombopoietin

Platelet functions such as aggregation and clot retraction are often abnormal in chronic mylogenous leukemia (CML) patients. However, the molecular mechanisms of these altered functions are unknown. As expression of the p210bcr-abl oncogene product, a constitutively active tyrosine kinase, is known to have an essential role in the pathogenesis of CML and tyrosine phosphorylation is intimately involved in various aspects of platelet activation, we examined the pattern of protein tyrosine phosphorylation in platelets from 15 CML patients by immunoblotting with a monoclonal antiphosphotyrosine antibody (4G10). Before and after stimulation with thrombin, the only consistent difference between normal and CML platelets was the presence of a tyrosine phosphorylated protein with a relative molecular weight of 39 kD. This tyrosine phosphorylated protein was identified as crid, an SH2, SH3 containing adapter protein. Thus, as previously demonstrated for neutrophils from CML patients, tyrosine phosphorylation of p39crkl persists in mature platelets. No tyrosine phosphorylation of crid was detected following stimulation with thrombin in normal platelets. However, crkl became incorporated into the Triton X-100 insoluble residue following thrombin stimulation in a manner dependent on platelet aggregation. Further, we found that crkl is an endogenous substrate for calpain, a protease that may be involved in postaggregation signaling processes. This suggests that crkl may be involved in the reorganization of the cytoskeleton during normal platelet aggregation and its tyrosine phosphorylation in CML platelets may contribute to the abnormal platelet function in CML patients. Finally, we found that thrombopoietin induces tyrosine phosphorylation of crk1 in normal platelets and FDCP cells genetically engineered to express human c-Mpl. This suggests that crk1 can be phosphorylated by a kinase other than p210bcr-abl and that crk1 may have a role in signaling by thrombopoietin.     

Interactions in the aetiology,presentation and management of synchronous and metachronous adenocarcinoma of the prostate and rectum

Adenocarcinoma of the prostate and rectum are common male pelvic cancers and may present synchronously or metachronously and, due to their anatomic proximity. The treatment of rectal or prostate cancer (in particular surgery and/or radiotherapy) may alter the presentation, incidence and management should a metachronous tumour develop. This review focuses on the interaction between prostatic and rectal cancer diagnosis and management. We have restricted the scope of this large topic to general considerations, management of rectal cancer after prostate cancer treatment and vice versa, management of synchronous disease and cancer follow-up issues.     

Circulatory responses to hypoglycaemia in diabetic and non‐diabetic children

The purpose of this study was to investigate the circulatory responses to hypoglycaemia in diabetic and non‐diabetic children and to determine whether these changes were associated with hormone levels or clinical variables. Plasma glucose levels in 18 diabetic and 15 control children were gradually lowered to 2.5 (0.3)?mmol/L (mean (SD)) and 2.9 (0.2)?mmol/L, respectively. Blood pressure and heart rate were recorded at 10‐min intervals, and blood samples were taken for hormone analysis. Systolic pressure increased from 110.1 (10.0) to 115.0 (11.2)?mmHg (p=0.008) in the diabetic children and from 116.9 (12.0) to 121.6 (12.7)?mmHg (p=0.049) in the controls. Diastolic pressure decreased from 61.9 (6.7) to 55.5 (7.6)?mmHg (p<0.001) in the diabetic children and from 66.5 (6.3) to 55.1 (5.1)?mmHg (p<0.001) in the controls. The increase in pulse pressure during hypoglycaemia was significantly smaller in the diabetic children (10.6 (5.5) vs. 15.7 (7.7)?mmHg, p=0.04). The final systolic and pulse pressure correlated with the final adrenaline level in the controls (r=0.66, p=0.008 and r=0.70, p=0.003, respectively). In the non‐diabetic as well as the diabetic group, the increase in pulse pressure correlated with the increase in adrenaline (r=0.66, p=0.008 and r=0.50, p=0.03, respectively). It is concluded that systolic pressure increases and diastolic pressure decreases during hypoglycaemia in children. The smaller increase in pulse pressure observed in the diabetic children is probably related to a significantly smaller increase in adrenaline in this group.     

Artifacts seen during CT pelvimetry: implications for digital systems with scanning beams

During computed tomography (CT) pelvimetry of two pregnant women, bony abnormalities of the fetuses were noted on the scout images that were not confirmed at delivery. To explore the cause of these artifacts, specimen long bones were manipulated in various ways during CT scout imaging. Artifacts like those seen during in vivo imaging were found to be caused by motion of the object. The CT scout view is an example of an image produced by a digital system that uses a scanning beam. This type of digital system is being used for several types of body imaging including screening for scoliosis and chest radiography. Attention to motion artifacts should decrease diagnostic errors and aid further development of these systems.     

In vivo growth of Epstein-Barr virus transformed B cells with mutations in latent membrane protein 2 (LMP2)

Summary.  Epstein-Barr virus (EBV) causes infectious mononucleosis in adolescents and is associated with malignant B lymphocyte proliferation in AIDS patients, patients undergoing immune suppression for organ transplantation, and SCID mice. In vitro, EBV transformed, latently infected lymphoblastoid B cell lines (LCLs) contain EBV episomes and express nine virus encoded proteins. Six are nuclear proteins (EBNAs) and three are the integral membrane proteins, LMP1, LMP2A, and LMP2B. To determine if LMP2 was essential for in vivo growth, SCID mice were injected with LCLs containing wild-type EBV (LMP2⁺) or with LCLs transformed with EBV containing mutations in either LMP2A or LMP2B (LMP2⁻). SCID mice injected with the LMP2⁺ or LMP2⁻ LCLs were monitored for tumor development, length of time to tumor development, and phenotypic characterization of the resulting tumors. No difference was observed in any of the above parameters between LMP2⁺ and LMP2⁻ LCLs demonstrating that LMP2 is not essential for the in vivo growth of EBV transformed B lymphocytes in SCID mice. Received July 19, 1996 Accepted October 15, 1996     

Early events in Epstein-Barr virus infection of human B lymphocytes.

The sequence of Epstein-Barr virus (EBV) and B lymphocyte changes in the 3 days following acute infection was analyzed. By 16 hr the average infected lymphocyte had 1 EBV episome. Nuclear protein-2 (EBNA-2) and EBNA-leader protein (-LP) were detected by 12 hr, and by 32 hr were at the levels of stable EBV infection in lymphoblastoid cell lines (LCLs). At 12 hr, all EBNA-LP and EBNA-2 RNAs were initiated from the Pw promoter. By 36 hr a significant EBNA-LP and EBNA-2 RNA fraction initiated from the upstream Pc promoter. Throughout acute infection, a similar fraction of potentially bicistronic EBNA-LP mRNAs had first exon splices which would result in EBNA-LP translation. By 36 hr c-myc RNA was transiently induced, and CD21 and CD23 RNAs were beginning to increase. This coincided with low-level EBNA-1, EBNA-3A, B, and C, and latent membrane protein-1 (LMP-1) expression. By 46 hr, EBNA-1, the EBNA-3s, and LMP-1 were near the levels ordinarily found in LCLs and a substantial fraction of lymphocytes were in S phase. These results are compatible with a key role for EBNA-2 (or EBNA-LP) in regulating virus and cell gene expression. High-level expression of the EBV-encoded small RNAs, EBERs, was delayed beyond 36 hr and may, therefore, be activated by other virus or cell genes. A 65-kDa virion protein persisted in acutely infected cells. This protein could be a mediator of virus or cell gene expression.