Asialo-von Willebrand factor inhibits platelet adherence to human arterial subendothelium: discrepancy between ristocetin cofactor activity and primary hemostatic function

Platelet adherence at high wall shear rates requires plasma von Willebrand factor (vWF). Clinically, the ristocetin cofactor (RCof) activity is the only widely available assay for vWF function. When purified vWF is treated with neuraminidase to yield asialo-vWF (AS- vWF), its RCof activity is increased by 20% to 40%. AS-vWF binds to normal human platelets independently of ristocetin and induces platelet aggregation in the presence of fibrinogen. To determine whether AS-vWF also shows an enhanced capacity to support platelet adherence to subendothelium, we used the Baumgartner technique. Intact vWF, AS-vWF, or AS-vWF treated with beta-galactosidase (asialo, agalacto-vWF; AS,AG- vWF) was added to normal citrated whole blood before perfusion over human umbilical artery segments (wall shear rate, 2,600 sec-1). Four micrograms per milliliter AS-vWF caused a 69% reduction in total platelet adherence compared with citrated whole blood (P less than .001), and 4 micrograms/mL AS,AG-vWF led to a 48% reduction (P less than .005). With 4 micrograms/mL intact vWF, the platelet adherence values were not significantly different from the controls. No significant differences in subendothelial platelet thrombi or postperfusion platelet counts were evident among any of the groups. In reconstituted afibrinogenemic perfusates, 4 micrograms/mL AS-vWF caused a 42% reduction in platelet adherence (P less than .05). Thus, AS-vWF is a potent inhibitor of platelet adherence, despite its enhanced RCof specific activity. Abnormalities in vWF carbohydrate may play a role in impaired primary hemostasis in some patients with von Willebrand's disease.     

Establishment of a human acute promyelocytic leukemia-ascites model in SCID mice

Acute promyelocytic leukemia (APL) is an interesting model for cancer research because of the presence of the specific PML-RARalpha fusion gene associated with the clinical response to retinoic acid differentiation therapy. To better understand and improve differentiation induction with retinoic acid, we have established a human APL-ascites model in SCID mice using the NB4 human APL cell line. NB4 (1 x 10(6) cells) were transplanted into the peritoneum (IP) of SCID mice for 1 month. NB4 ascites cells (A-NB4) appeared, which were then engrafted in SCID mice periodically for 18 passages at an interval of 3 to 4 weeks with a 100% success rate of tumor induction. The mean survival times of SCID mice transplanted with 1 x 10(6) A-NB4 cells was 21.6 +/- 2.3 days. Analysis of the biologic characteristics of ninth passage NB4 ascitic cells was performed and they were found to have the morphologic, immunologic, cytogenetic, and molecular features of cultured NB4 cells. Furthermore, A-NB4 cells were capable of differentiating when treated with all-trans retinoic acid (ATRA), as manifested by enhanced NBT reduction and CD11b expression. In vivo treatment with ATRA in SCID mice for 4 days also increased NBT reduction by A-NB4 cells. ATRA treatment significantly prolonged survival time in the group after transplantation (28.1 +/- 6.8 to 29.1 +/- 8.4 days) compared with the control (P < .001). Furthermore, treatment with adriamycin, an effective chemotherapeutic drug in APL, had a strong growth suppressive effect on A-NB4 cells. These results demonstrate that this SCID-APL (NB4 ascites cells) model is a useful preclinical system for evaluating new or known drugs in the treatment of APL.     

Spinal cord compression–do we miss it?

Four children with spinal cord compression due to malignant tumours are presented. The severity of the condition was not initially recognized by parents, or the nature of the likely cause by the initial physicians. Lower limb asymmetrical weakness, clear-cut sensory levels, and marked pain indicate need for urgent imaging and exclusion of a space occupying lesion. In 1997 diagnosis of Guillain-Barré syndrome should not be made without careful prior spinal imaging.     

Outpatient lumbar myelography. Initial results in 79 examinations using a low-dose metrizamide technique

Seventy-nine patients underwent lumbar myelography on an outpatient basis, with a low (3.75 g) dose of metrizamide as the radiocontrast agent and a 25-gauge spinal needle used for lumbar puncture. No patient experienced significant neurotoxicity following the examination; 70.8% (56 of 79) experienced minimal (23%) or no (48%) side effects. Three patients (3.8%) were admitted to the hospital for management of common side effects (headache, nausea/vomiting, back pain). We obtained postmyelographic computed tomographic scans on 96% (76 of 79) of the patients. Our initial results suggest that outpatient lumbar myelography is safe and can be performed with a very acceptable incidence of side effects.     

Platelet adhesion to collagen types I through VIII under conditions of stasis and flow is mediated by GPIa/IIa (alpha 2 beta 1-integrin)

Platelet adhesion to fibrillar collagens (types I, II, III, and V) and nonfibrillar collagens (types IV, VI, VII, and VIII) was investigated in the presence of physiologic concentrations of divalent cations under conditions of stasis and flow. Under static conditions, platelet adhesion was observed to collagen types I through VII but not to type VIII. Under flow conditions, platelet adhesion to collagen types I, II, III, and IV was almost independent of shear rates above 300/s. Collagen type V was nonadhesive. Platelet adhesion to collagen type VI was shear rate-dependent and optimal at a rate of 300/s. Collagen types VII and VIII showed minor reactivity and supported platelet adhesion only between shear rates 100 to 1,000/s. Monoclonal antibody (MoAb) 176D7, directed against platelet membrane glycoprotein Ia (GPIa; very late antigen [VLA]-alpha 2 subunit), completely inhibited platelet adhesion to all collagens tested, under conditions of both stasis and flow. Platelet adhesion to collagen type III at shear rate 1,600/s was only inhibited for 85%. The concentration of antibody required for complete inhibition of platelet adhesion was dependent on the shear rate and the reactivity of the collagen. An MoAb directed against GPIIa (VLA-beta subunit) partially inhibited platelet adhesion to collagen. These results show that GPIa-IIa is a major and universal platelet receptor for eight unique types of collagen.