The Lysosomal Granule Membrane Protein, Lamp-2, Is also Present in Platelet Dense Granule Membranes

Lysosomal Associated Membrane Protein-2 (LAMP-2) is an inherent component of lysosomal granule membranes in diverse cell types, including platelets. We examined platelets for evidence of LAMP-2 in dense granule membranes as CD63 has previously been shown to be present in both lysosomal and dense granule membranes. Immunological techniques were used to examine the localization of LAMP-2 in control platelets and those from an individual with Hermansky-Pudlak syndrome (HPS), a condition characterised by platelet dense granule deficiency. Immunoblotting studies demonstrated that LAMP-2 was enriched in a dense granule preparation. Flow cytometry of thrombin-stimulated control platelets was consistent with biphasic surface expression of LAMP-2. The early expression was accompanied by dense granule, but minimal lysosomal granule, release. The late expression was accompanied by additional lysosomal granule release only. Thrombin stimulation of HPS platelets showed only late, lysosome-associated LAMP-2 expression. Immunoelectron microscopy indicated the presence of LAMP-2 in the membranes of serotonin-containing granules as identified by an anti-serotonin polyclonal antibody. These data indicate that LAMP-2 is present in the membranes of platelet dense granules in addition to lysosomal granules, and has a similar distribution to CD63.

Laboratory testing for platelet function disorders

Platelet function testing is both complex and labor intensive. A stepwise approach to the evaluation of patients with suspected platelet disorders will optimize the use of laboratory resources, beginning with an appropriate clinical evaluation to determine whether the bleeding is consistent with a defect of primary hemostasis. Bleeding assessment tools, evaluation of platelet counts, and review of peripheral blood cell morphology can aid the initial assessment. For patients requiring further laboratory testing, platelet aggregometry, secretion assays, and von Willebrand factor assays are the most useful next steps and will direct further specialized testing including flow cytometry, electron microscopy, and molecular diagnostics. Guidelines and recommendations for standardizing platelet function testing, with a particular focus on light transmission aggregometry, are available and can provide a template for clinical laboratories in establishing procedures that will optimize diagnosis and assure quality results. This review outlines an approach to platelet function testing and reviews testing methods available to clinical laboratories.

von Willebrand disease and platelet disorders

The diagnosis and management of bleeding disorders is made difficult by the complexity and variety of disorders, clinical symptoms and bleeding type and severity. von Willebrand disease (VWD) and platelet disorders are disorders of primary haemostasis and together represent the most common inherited bleeding disorders. In this article, we describe the diagnosis of VWD and platelet disorders and the treatment options for VWD.

Musculoskeletal health of subjects with hemophilia A treated with tailored prophylaxis: Canadian Hemophilia Primary Prophylaxis (CHPS) Study

BACKGROUND

Full-dose prophylaxis is very effective at minimizing joint damage but is costly. Tailored prophylaxis has been proposed as a way of reducing costs while still protecting joints.

OBJECTIVE

To report detailed findings in index joints of 56 subjects with severe hemophilia A entered into the Canadian Hemophilia Prophylaxis Study, and treated with tailored prophylaxis, after 13 years.

METHODS

Boys with severe hemophilia A (< 2% factor) and normal joints were enrolled between the ages of 1 and 2.5 years. Initial treatment consisted of once-weekly factor infusions, with the frequency escalating in a stepwise fashion when breakthrough bleeding occurred. During the first 5 years, subjects were examined every 3 months using the modified Colorado Physical Evaluation (PE) scale; subsequently, every 6 months. The Childhood Health Assessment Questionnaire (CHAQ) was administered at each visit.

RESULTS

Median age at study entry was 19 months (range 12-30 months); median follow-up was 92 months (range 2-156). The median PE score was 2, 3 and 3 at ages 3, 6 and 10 years. Persistent findings were related to swelling, muscle atrophy and loss of range of motion. The median score for each of these items (for the six index joints) was 0 at ages 3, 6 and 10 years. The median overall CHAQ score was 0 at ages 3, 6 and 10 years, indicating excellent function.

CONCLUSIONS

Canadian boys treated with tailored primary prophylaxis exhibit minimal joint change on physical examination and minimal functional disability.

Inherited disorders of platelet function and challenges to diagnosis of mucocutaneous bleeding

SUMMARY

Platelets play a pivotal role in the arrest of bleeding at sites of vascular injury. Following endothelial damage, they respond rapidly by adhesion to subendothelial matrix proteins resulting in platelet activation, spreading, aggregation, secretion and recruitment of additional platelets to form the primary haemostatic plug. This mass provides a surface for thrombin generation and fibrin mesh formation that stabilizes the clot. Careful study of patients with inherited platelet disorders and, subsequently, of informative animal models, has identified structural platelet abnormalities that have enhanced our understanding of platelet function. The investigations of rare, but severe, inherited platelet disorders have led us to the discovery of causative molecular defects. One of the most informative is the rare autosomal recessive disorder Glanzmann thrombasthenia, caused by defect or deficiency in the platelet integrin alphaIIbbeta3, resulting in absent platelet aggregation and a significant clinical bleeding diathesis. Our new challenge is to understand the mechanisms underlying more common, but less well-defined, mucocutaneous bleeding (MCB) disorders. Present diagnostic testing for platelet function disorders and von Willebrand's Disease often fails to identify the cause of bleeding in individuals with inherited MCB.

Incorporation of map kinases into the platelet cytoskeleton

Erk1 (p44) and erk2 (p42) mitogen-activated protein (MAP) kinases are activated in agonist-stimulated platelets, although their role(s) in the activation process is unknown. In the present study, erk1, erk2 and the phosphorylated forms of both enzymes became associated with the contractile cytoskeleton in thrombin-stimulated platelets. Enzyme incorporation was accompanied by an increase in MAP kinase activity in the cytoskeleton, which was inhibited by PD98059. Pretreatment of the platelets with the arginine-glycine-aspartic acid-serine (RGDS) polypeptide enhanced both the cytoskeletal association and the enzyme activity, but cytochalasin D had no significant effect. Platelets from a patient with Glanzmann's thrombasthenia lack the alpha(IIb)beta(3) integrin and form only a rudimentary cytoskeleton, however, this cytoskeleton is enriched with both erk1 and erk2. These data suggest either that MAP kinases play a role in cytoskeletal rearrangement or that the cytoskeleton act as a frame to align MAP kinases with substrates in a highly integrated signal transduction pathway.

Evaluation of primary hemostasis in neonates with a new in vitro platelet function analyzer

With the use of the PFA-100 platelet function analyzer to evaluate primary hemostasis in whole blood, measured as closure time (CT), neonates had shorter CTs than members of an adult control group. Multivariate analysis of measures that contribute to primary hemostasis showed that higher hematocrits and increased ristocetin cofactor activity were the best correlates for CTs of cord blood. These 2 factors may also enhance primary hemostasis in vivo and compensate for the impaired platelet function of the newborn.

CD63 associates with the alphaIIb beta3 integrin-CD9 complex on the surface of activated platelets

The tetraspanins are integral membrane proteins expressed on cell surface and granular membranes of hematopoietic cells and have been identified in multi-molecular complexes with specific integrins. In resting platelets, CD63, a member of the tetraspanin superfamily, is present in dense granule and lysosomal membranes and, following platelet activation, translocates to the plasma membrane. In the present study, platelet activation by thrombin leads to incorporation of CD63 into the Triton-insoluble actin cytoskeletal fraction. This incorporation was inhibited by preincubation of platelets with RGDS or EGTA and did not occur in platelets from a patient with Glanzmann's thrombasthenia, suggesting that it was dependent upon alphaIIbbeta3. In activated platelets, the anti-CD63 MoAb, D545, co-immunoprecipitated CD63 with other surface-labeled proteins, including alphaIIbbeta3 and another tetraspanin, CD9. The association of CD63 with CD9 and alphaIIbbeta3, was not inhibited by preincubation of platelets with RGDS or EGTA. D545 did not inhibit the adhesion of activated platelets to purified extracellular matrix proteins, but significantly decreased adhesion of thrombin-activated platelets to neutrophils in a rosetting assay. D545 also caused disaggregation of platelets stimulated by ADP, but had no effect on aggregation induced by other agonists. These results are consistent with the proposal that CD63 becomes part of an alphaIIbbeta3-CD9-CD63 integrin-tetraspanin complex in activated platelets--an association that may modulate the function of alphaIIbbeta3-dependent interaction with other cells such as neutrophils.

Alpha1-antitrypsin deficiency with fatal intracranial hemorrhage in a newborn

A 4-week-old boy had a fatal intracranial hemorrhage resulting from vitamin K deficiency. The infant had received no vitamin K prophylaxis and was exclusively breastfed. At autopsy, examination of the liver showed cholestasis and fibrosis. DNA was isolated from a blood spot on a Gutherie sample card obtained from the infant for routine metabolic screening. This DNA was used for alpha1-antitrypsin genotyping studies. Genotyping studies identified homozygosity for the point mutation 9989G-->A, confirming a diagnosis of alpha1-antitrypsin deficiency (ZZ phenotype), and resulted in appropriate screening of siblings born after this child's death. Alpha1-antitrypsin deficiency should be considered in the differential diagnosis of infants with late hemorrhagic disease of the newborn. Use of blood from the metabolic screening card as a source of DNA allowed confirmation of this diagnosis after the infant's death.

Platelet dense granules: structure, function and implications for haemostasis

The advances that have been made over the last decade in microscopic, biochemical, molecular, and genetic techniques have led to substantial improvement in our understanding of platelet dense granule structure and function, and the implications of dense granule deficiencies for haemostasis. However, much has still to be learned. For example, what is the specific mechanism of docking and fusion that occurs during dense granule exocytosis? What are the roles of dense granule membrane proteins during exocytosis or after expression on the surface of activated platelets? Finally, how do the genetic defects identified in HPS and CHS result in the clinical phenotype of these diseases, and what does this tell us about the origin and function of the affected subcellular organelles?

Impaired signal transduction in neonatal platelets

Previous in vitro studies of cord blood platelets from full-term and preterm neonates have demonstrated decreased responses to most physiologic agonists. This hyporesponsiveness is, in part, related to both deficient synthesis of, and response to, an important mediator of platelet function, thromboxane A2(TxA2). The poor response of neonatal platelets to TxA2 is not due to differences in TxA2 receptor binding characteristics, when compared with platelets from adult controls. Therefore, the postreceptor signal transduction pathway was investigated. The TxA2 receptor is linked via the trimeric GTP-binding protein, Gq, to phospholipase C-beta (PLC beta), and stimulation of platelets with the stable TxA2 mimetic, U46619, leads to activation of PLC beta and subsequent intracellular signaling events. U46619-induced 32P-phosphatidic acid formation, an index of PLC beta activation, was decreased in platelets of neonates (166 +/- 10%) when compared with adult controls (206 +/- 22%) (p < 0.05). Mobilization of intracellular calcium was impaired in platelets of newborns (175 +/- 49 nM) in comparison to adult controls (506 +/- 130 nM) (p < 0.01), after stimulation with U46619. U46619-stimulated GTPase activity was blunted in platelet membrane fractions from full-term neonates and almost absent in platelet membranes from preterm infants. Immunoblotting studies of the platelet membrane fractions, quantified by densitometric analysis, showed that levels of the G alpha q subunit were not significantly different between adult and neonate, and were not the cause of the marked differences in GTPase activity. These data suggest that signal transduction through the TxA2 receptor is affected by decreased activity of Gq in platelets of neonates, and that this defect in signal transduction through PLC beta contributes to the observed poor response of newborns' platelets to TxA2 and consequently to TxA2-dependent agonists such as collagen.

Familial neuroblastoma: report of a kindred with later age at diagnosis

PURPOSE

To describe the clinical and biologic features of neuroblastoma (NB) in two siblings and their maternal second cousin.

PATIENTS AND METHODS

NB was diagnosed in the siblings at 2 1/2 (patient 2) and 5 (patient 3) years of age. NB was diagnosed in their maternal second cousin (patient 1) when she was 7 years old. Standard clinical and biological data, tumor karyotype, and tumor allelotype at select loci were obtained.

RESULTS

Patient 1 had International Neuroblastoma Staging System (INSS) stage 4 NB and unfavorable histology but no evidence of MYCN amplification; she died from complications of autologous bone marrow transplantation in second remission. Patient 2 had INSS stage 4 NB with unfavorable histology but no MYCN amplification; her disease recurred 39 months after completing therapy. Patient 3 had INSS stage 1 NB with favorable biologic features; he was treated with surgical excision and remains free of disease.

CONCLUSIONS

Familial NB may occur at a later age than predicted by the tumor suppressor gene model of inherited cancer. This report further emphasizes the clinical and biological heterogeneity of familial NB.

Effects of the mitogen-activated protein (MAP) kinase kinase inhibitor 2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one (PD98059) on human platelet activation

The role of mitogen-activated protein (MAP) kinase cascades in platelet function remains to be determined. Several studies have suggested a role in the activation of phospholipase A2; however, other functions seem likely. The object of the present study was to determine the role of the MAP kinase cascade in platelet function. An inhibitor of the mitogen-activated protein kinase kinase MEK1, 2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one (PD98059), was used, at concentrations consistent with those reported to inhibit MEK1, to examine the role that this enzyme plays in platelet function. PD98059 inhibited aggregation in response to low-dose collagen and arachidonic acid, but not that in response to high-dose collagen, thrombin, thrombin receptor-activating peptide (TRAP), 9,11-dideoxy-11alpha, 9alpha-epoxymethano-prostaglandin F2alpha (U46619), or phorbol ester. Thrombin, thrombin receptor-activating peptide, U46619, collagen, and arachidonic acid each caused the release of [3H]serotonin from dense granules, but only that elicited by low-dose collagen and arachidonic acid was inhibited by PD98059. The release of [3H]arachidonic acid in response to thrombin or collagen was unaffected by PD98059 pretreatment. In contrast, collagen- and arachidonic acid-induced thromboxane formation was inhibited by PD98059. These data suggest that MEK1 is not involved in the platelet response to thrombin or U46619. Furthermore, the inhibitory effects of PD98059 on collagen- and arachidonic acid-induced responses suggest that PD98059 may inhibit the conversion of arachidonic acid to thromboxane, in addition to its reported effects on MEK1.

Continuous infusion of porcine factor VIII in the management of patients with factor VIII inhibitors

The effectiveness of continuous infusion porcine factor VIII (PFVIII) has been evaluated in the treatment of 7 consecutive patients with factor VIII(FVIII) inhibitors. Two patients had hemophilia A and five were nonhemophiliacs with acquired FVIII inhibitors. The median pretreatment anti-porcine FVIII titre was 0.2 (range: 0-15.0) Bethesda units (BU), and the anti-human FVIII titer was 12.0 BU (range: 2.4-50.0). All patients presented with major bleeding. Patients were given a bolus dose of PFVIII followed by continuous infusion. Six patients also received immunosuppressive therapy. Therapeutic FVIII levels (>0.5 U/ml) were achieved in 6 of 7 patients at a median time of 12.5 hr, and then maintained with continuous infusion PFVIII. Six patients were treated for more than 7 days, and in four of these there was a decline in FVIII recovery between days 7 to 11, presumably related to a rising antibody response to PFVIII. These four patients were plasmapheresed and the three patients with autoantibodies recovered therapeutic FVIII levels but this did not occur in the patient with hemophilia. Thrombocytopenia developed in 4 patients at days 18 to 24, with the platelet count falling to 11 to 87 x 10(9)/L, and the PFVIII was discontinued in 3 patients. All patients recovered from the acute bleeding events. With prolonged immunosuppressive therapy, the FVIII inhibitor disappeared in all patients with autoantibodies and there have been no relapses after a median follow-up period of 581 days. This study demonstrates that continuous infusion PFVIII is an effective therapy for patients with FVIII inhibitors, but that prolonged treatment is associated with the development of inhibitors to porcine FVIII and severe thrombocytopenia, which readily corrects with discontinuation of PFVIII.

Acquired inhibitors to factors V and X after exposure to topical thrombin: interference with monitoring of low molecular weight heparin and warfarin

Repeated surgical exposure to topical bovine thrombin is known to be associated with the development of antibodies to bovine and human thrombin and factor V. This is demonstrated by abnormalities of in vitro coagulation assays and, rarely, postoperative bleeding. We describe a 4-year-old child in whom an antibody to bovine factor X developed after cardiac surgery; this antibody interfered with the heparin anti-Xa assay, thereby complicating the monitoring of heparin therapy.

Deficient thromboxane synthesis and response in platelets from premature infants

In vitro function of cord blood platelets from 35 premature infants (gestational age 32 +/- 3.2 wk) was compared with that of 12 full-term infants and 14 adult control subjects. In comparison with adult platelets, preterm platelets showed impaired aggregation, in response to thrombin, collagen, ADP, and U46619 [a stable analog of thromboxane A2 (TxA2)], and impaired [14C]serotonin secretion in response to collagen and U46619. The production of TxB2 (the stable TxA2 metabolite) in response to collagen was reduced in preterm platelets (30.2 +/- 5.5 ng/mL) compared with full-term (52.7 +/- 12.6 ng/mL) or adult control platelets (132.3 +/- 38.7 ng/mL). The deficient TxB2 production and U46619 response prompted further investigation of TxA2 receptor number and binding characteristics. Immunoblotting using an anti-TxA2 receptor antibody (anti-P2) identified a single, identical 55-kD band in solubilized membranes of control, full-term, and preterm platelets. Flow cytometry using anti-P2 produced histograms that did not differ between adults and neonates. Ligand binding studies using [3H]U46619 were carried out on 10 samples from each group. Scatchard analysis yielded a single class of binding sites with no significant difference among the Kd values (85 +/- 16 versus 99 +/- 12 versus 100 +/- 12 nM) or number of binding sites per platelet (1876 +/- 460 versus 2450 +/- 478 versus 2777 +/- 536) for preterm and full-term infants and adults. Therefore platelets of preterm infants show impaired TxA2 production and response. The poor response is not related to altered binding characteristics of the TxA2 receptor but may lie in the postreceptor signal transduction pathway.

The lysosomal granule membrane protein, LAMP-2, is also present in platelet dense granule membranes

Lysosomal Associated Membrane Protein-2 (LAMP-2) is an inherent component of lysosomal granule membranes in diverse cell types, including platelets. We examined platelets for evidence of LAMP-2 in dense granule membranes as CD63 has previously been shown to be present in both lysosomal and dense granule membranes. Immunological techniques were used to examine the localization of LAMP-2 in control platelets and those from an individual with Hermansky-Pudlak syndrome (HPS), a condition characterised by platelet dense granule deficiency. Immunoblotting studies demonstrated that LAMP-2 was enriched in a dense granule preparation. Flow cytometry of thrombin-stimulated control platelets was consistent with biphasic surface expression of LAMP-2. The early expression was accompanied by dense granule, but minimal lysosomal granule, release. The late expression was accompanied by additional lysosomal granule release only. Thrombin stimulation of HPS platelets showed only late, lysosome-associated LAMP-2 expression. Immunoelectron microscopy indicated the presence of LAMP-2 in the membranes of serotonin-containing granules as identified by an anti-serotonin polyclonal antibody. These data indicate that LAMP-2 is present in the membranes of platelet dense granules in addition to lysosomal granules, and has a similar distribution to CD63.

Deposition of transforming growth factor-beta in the marrow in myelofibrosis, and the intracellular localization and secretion of TGF-beta by leukemic cells

The marrows of 10 patients with hematologic malignancies were examined by immunohistochemistry using anti TGF-beta antibody, CC(1-30), which detects secreted TGF-beta, and compared with four normal marrows. TGF-beta was not demonstrated in marrows with a normal level of reticulin fibrosis; however, TGF-beta was observed within collagen in marrows having collagen fibrosis or increased reticulin fibrosis. The extent of TGF-beta deposition paralleled the severity of fibrosis (P < .0001), and occurred even with normal or reduced numbers of megakaryocytes. Using another TGF-beta antibody, LC(1-30), which detects intracellular TGF-beta, TGF-beta was detected by immunofluorescence in discrete sites in the cytoplasm of immature and mature myeloid and large granular lymphocytic leukemia cells. These sites colocalized with areas detected by an anti-granule antibody (D545) suggesting that TGF-beta was stored in granules. However, neither the TGF-beta mRNA content nor the degree of TGF-beta secretion by these leukemic cells correlated with the extent of TGF-beta deposition in the marrow. Thus, TGF-beta deposition in marrow may contribute to myelofibrosis, but the source of this cytokine in the absence of megakaryocytes requires further study.

Development of antibodies to bovine and human factor V in two children after exposure to topical bovine thrombin

PURPOSE

Acquired inhibitors to coagulation factors are rare in pediatric patients. Exposure to topical bovine thrombin is a risk factor for the development of inhibitors in adult cardiac surgery patients. We report two pediatric patients who developed inhibitors to bovine and human factor V after exposure to fibrin glue containing bovine thrombin.

PATIENTS AND METHODS

The two patients, ages 3 1/2 years and 10 months, were studied after cardiac surgery. One patient had clinical bleeding. Coagulation factor assays and inhibitor studies were performed.

RESULTS

The presence of a circulating inhibitor to bovine factor V was observed in both patients and to human factor V in one patient. The inhibition of bovine factor V interfered with standard assays for factor VIII activity using a commercial substrate fortified with bovine factor V resulting in spurious factor VIII deficiency. In one patient, an inhibitor of bovine thrombin was also identified. The inhibition of human factor V activity in one patient may have contributed to clinical bleeding.

CONCLUSIONS

Pediatric patients exposed to topical bovine thrombin, particularly in the setting of cardiac surgery, are at risk for the development of antibodies to bovine thrombin and factor V. This may also result in apparent but spurious depletion of other coagulation factors. These antibodies may cross-react with human coagulation factors, particularly factor V, resulting in clinical bleeding.

Primary hypothyroidism with intracranial hypertension and pituitary hyperplasia

A 12-year-old girl presented with primary hypothyroidism, secondary pituitary hyperplasia, and intracranial hypertension. Cranial computed tomography revealed a sellar mass with suprasellar extension. She responded to medical treatment. Intracranial hypertension may be associated with primary hypothyroidism prior to thyroxine treatment. Because significant pituitary hyperplasia can be associated with primary hypothyroidism, it is vital to have endocrine investigation prior to consideration of surgical removal of an apparent pituitary tumor.

The empty sack syndrome: a platelet storage pool deficiency associated with empty dense granules

Two sisters with lifelong bleeding tendencies were examined to determine whether their condition was associated with a platelet defect. Their platelet aggregation in response to epinephrine and collagen was abnormal, and the secretion of serotonin and ATP was markedly reduced. The platelet contents of serotonin, ADP, and ATP were all diminished and the ATP:ADP ratio was increased. Direct enumeration by whole-mount and quinacrine-fluorescence techniques demonstrated that the platelets from both sisters had significantly fewer dense granules than controls. These characteristics are similar to an individual with Hermansky-Pudlak syndrome and are consistent with a platelet dense granule deficiency. In contrast, immunofluorescence studies using an antibody against the dense granule membrane protein granulophysin suggested that both sisters had numbers of granules within the normal range. Evaluation by immunoblotting and ELISA indicated the presence of normal levels of granulophysin in the platelets from both sisters; FACS analysis demonstrated the surface expression of granulophysin under conditions of selective dense granule release. These results are consistent with these sisters having a form of dense granule storage pool deficiency where the granular membranes are present but the granules have reduced contents. This observation represents a novel form of storage pool disease which we have termed the empty sack syndrome.

Role of transforming growth factor-beta in chronic lymphocytic leukemia

TGF-beta is an important immunoregulator as it suppresses proliferation and function of B- and T-lymphocytes. In the present study we have examined the cellular localization and secretion of TGF-beta in B-cells from normal donors and patients with CLL and have assessed the influence of TGF-beta 1 on DNA synthesis in these cells. Using anti-LC(1-30)--a polyclonal anti-TGF-beta 1 antibody--TGF-beta was localized to discrete sites within the cytoplasm of both normal and malignant lymphocytes. These areas co-localized with areas detected by an antigranule antibody (D545), suggesting that TGF-beta may be stored within cytoplasmic secretory vesicles. Both normal B- and CLL cells contained low or undetectable levels of TGF-beta mRNA and secreted low and equivalent amounts of TGF-beta. Compared to untreated cells, DNA synthesis was reduced by TGF-beta 1 to a mean +/- S. E. of 0.84 +/- 0.07 in CLL cells and this was significantly less (p < 0.001) than that observed in normal B-cells (mean +/- S. E. of control, 0.12 +/- 0.02). In 3 of the 18 patients, TGF-beta 1 stimulated DNA synthesis. The reduced inhibition of leukemic cell DNA synthesis by TGF-beta 1 in CLL may provide these cells with a growth or survival advantage over normal lymphocytes and contribute to their selective accumulation.

Quantification of a novel dense granule protein (granulophysin) in platelets of patients with dense granule storage pool deficiency

An antigen-capture sandwich enzyme-linked immunosorbent assay (ELISA) was developed for a novel protein granulophysin, a constituent of the platelet dense granule (DG) membrane and used to characterize patients with dense granule storage pool deficiency (delta-SPD). The assay uses two monoclonal antibodies against the protein, one of which is conjugated to peroxidase. Purified DGs, an enriched source of the protein, were used for the standard curve. Granulophysin levels were only low in forms of delta-SPD associated with albinism. Granulophysin levels in platelet homogenates of 30 patients with the Hermansky-Pudlak syndrome form of delta-SPD were 1/4 to 1/5 of levels in controls or obligate heterozygotes. Two patients with the Chediak-Higashi form of delta-SPD syndrome also had markedly reduced levels of granulophysin. Patients with other forms of delta-SPD had normal levels of granulophysin. Two sisters with delta-SPD in one family had normal granulophysin present in empty dense granule membrane vesicles. Three members of another family with delta-SPD had low DG counts but normal granulophysin levels, indicating that in this group the level of granulophysin was maintained despite the reduction in granule formation. Thus, granulophysin quantitation facilitates characterization of delta-SPD patients and may provide clues to the nature of defective granules in delta-SPD subtypes.

Platelet dense granule membranes contain both granulophysin and P-selectin (GMP-140)

We recently reported the characterization of a platelet granule membrane protein of molecular weight (mol wt) 40,000 called granulophysin (Gerrard et al: Blood 77:101, 1991), identified by a monoclonal antibody (MoAb D545) raised to purified dense granule membranes. Using immunoelectron-microscopic techniques on frozen thin sections, this protein was localized in resting and thrombin-stimulated platelets. In resting platelets, labeled with antigranulophysin antibodies and immunogold probes, label was localized to the membranes of one or two clear granules per platelet thin section. D545 also labeled dense granules in permeabilized whole platelets and isolated dense granule preparations examined by whole-mount techniques. Expression of granulophysin on the platelet surface paralleled dense granule secretion as measured by 14C-serotonin release under conditions in which lysosomal granule release, as measured by beta-glucuronidase secretion, was less than 5%. After thrombin stimulation, both the surface-connected canalicular system and the plasma membrane were labeled, demonstrating redistribution of granulophysin associated with degranulation. Double labeling experiments with D545 and antibodies to the alpha-granule membrane protein, P-selectin, demonstrated labeling of both P-selectin and granulophysin on dense granule membranes. Distribution of both proteins on the plasma membrane after platelet stimulation was similar. The results demonstrate that granulophysin is localized to the dense granules of platelets and is redistributed to the plasma membrane after platelet activation.

Inherited platelet-storage pool deficiency associated with a high incidence of acute myeloid leukaemia

A family with an inherited bleeding disorder extending over four generations, and multiple cases of myeloblastic and myelomonoblastic leukaemia was studied. Ten members of the family had, by history, a haemorrhagic diathesis. There were three documented cases of myeloblastic leukaemia, two documented cases of myelomonoblastic leukaemia and two more cases of leukaemia by history. In four of the cases the bleeding diathesis clearly antedated the leukaemia, in two by many years. The bleeding disorder is characterized by a long bleeding time, abnormal platelet aggregation, low platelet ADP and decreased numbers of platelet dense bodies consistent with a dense granule storage pool deficiency. The number of dense granules was decreased by immunofluorescence employing quinacrine or using an antibody to the dense granule membrane protein, granulophysin, confirming an absolute decrease in dense granule numbers rather than the presence of empty granule sacs. This congenital storage pool deficiency is associated with a high incidence of acute myeloid leukaemia in this family.

Identification of a platelet dense granule membrane protein that is deficient in a patient with the Hermansky-Pudlak syndrome

Monoclonal antibodies were raised after injecting mice with isolated human dense granules. Several of these monoclonals were found to recognize a 40-Kd dense granule membrane protein. Western blot and immunofluorescent analysis confirmed the dense-granule specificity. After thrombin activation, the protein was found in patches on the external platelet membrane. By Western blot and slot blot analysis, the protein was found to be markedly deficient in a patient with the Hermansky-Pudlak syndrome. Studies of neutrophils and endothelial cells show the presence of immunologically related granule-membrane protein(s). Western blots using four anti-synaptophysin antibodies and three antibodies to the platelet 40-Kd protein suggest that the protein may share some homology with, but is not identical to, the synaptosomal membrane protein synaptophysin.

Studies in patients with bleeding disorders show that platelet-vessel interaction is important for thromboxane formation in bleeding time wounds

The production of thomboxane B2, the primary metabolite of thromboxane A2, and 6-keto prostaglandin F1 alpha, the primary metabolite of prostacyclin, were measured in response to a standardized vascular injury, the bleeding time, in patients with von Willebrand's disease and in patients with platelet function defects. Compared to controls, thromboxane B2 levels in bleeding time blood were significantly lower in subjects with von Willebrand's disease. In patients with platelet function defects associated with a deficient response to thromboxane A2, thromboxane B2 production in bleeding time blood was similar to controls. In subjects with other platelet function defects, thromboxane production was significantly lower than normal. 6-keto PGF1 alpha production in bleeding time blood was not significantly different in patients compared to controls. The results suggest that bleeding time thromboxane production is influenced by the extent of platelet-vessel interaction.

Platelet storage pool deficiency: diagnosis in patients with prolonged bleeding times and normal platelet aggregation

We evaluated 46 patients with prolonged bleeding times, and no demonstrable abnormalities of either von Willebrand factor or platelet aggregation, for possible deficiency of platelet storage pool. Studies of ATP release from thrombin-stimulated platelets and enumeration of dense granules in platelet whole mounts were performed in these patients. Seventeen patients (35%) had both decreased ATP release and decreased numbers of dense granules, suggesting the presence of a storage pool defect. Thus, storage pool deficiency may be present in the absence of the classical aggregation abnormalities. Evidence of storage pool deficiency should be considered in all patients with an isolated unexplained prolongation of the bleeding time. The methods used in this study are readily applicable to most clinical laboratories.

Deficient collagen-induced activation in the newborn platelet

We have investigated the impaired secretion response of neonatal platelets. We compared the response of washed neonatal and adult platelets to thrombin and collagen, and to specific activators of calcium flux (inositol trisphosphate) and protein kinase C activation (oleoyl-acetyl glycerol). Neonatal platelets show no impairment of aggregation, secretion of [14C]serotonin or phosphorylation of specific intracellular proteins in response to thrombin, inositol trisphosphate, or oleoyl-acetyl glycerol. However, neonatal platelets have a markedly decreased response to collagen. To further evaluate this deficient response, we examined specific aspects of the collagen activation pathway. Collagen-platelet interaction as measured by adhesion of platelets to collagen-coated dishes showed no difference in adhesion of neonatal platelets compared to adult controls (20.1 +/- 11.6 versus 18.6 +/- 9.3%). The presence of GPIa/IIa, a Mg2(+)-dependent collagen receptor, was evaluated by flow cytometric analysis of binding of fluorescein-tagged monoclonal antibody, 6F1 (directed against GPIa/IIa). There was no difference either in the percent of platelets that bound antibody (80 versus 81%) or in the mean fluorescence intensity of the adult and neonatal samples. Phosphoinositide hydrolysis was decreased in neonatal platelets in response to collagen but normal in response to thrombin. Neonatal platelets released more arachidonic acid than adult platelets in response to thrombin (29.5 +/- 3.2 versus 19.6 +/- 1.8%) but less than adult platelets in response to 10 micrograms/mL collagen (3.2 +/- 1.1 versus 9.3 +/- 3.0%).(ABSTRACT TRUNCATED AT 250 WORDS)

A role for protein kinase C in the membrane fusion necessary for platelet granule secretion

The addition of 1-oleoyl-2-acetylglycerol (OAG), or phorbol-12-myristate-13-acetate (PMA) to platelets induced the phosphorylation of a 47,000 dalton protein (47 Kd), fusion of granule membranes with membranes of the surface connected canalicular system, the formation of large vesicles and the secretion of serotonin. 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine (H7), and sphingosine, inhibitors of protein kinase C, significantly inhibited the ultrastructural changes and the phosphorylation of 47 Kd. N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA1004), structurally similar to H7, but a weaker inhibitor of protein kinase C, did not attenuate these responses to OAG or to PMA. H7, but not HA1004, also markedly inhibited secretion induced by the synergistic combination of OAG and the calcium ionophore A23187. Amiloride and 5-(N,N dimethyl)-amiloride, inhibitors of the Na+/H+ transporter, did not inhibit the ultrastructural response and the protein phosphorylation induced by OAG, or the secretion induced by the combination of A23187 and OAG. The results link the activation of protein kinase C by diglycerides to the labilization and fusion of granule membranes important for secretion.

A reassessment of the bleeding time: association of age, hematocrit, platelet function, von Willebrand factor, and bleeding time thromboxane B2 with the length of the bleeding time

In order to provide an overview of the relative contribution of platelet, von Willebrand factor, and other abnormalities to patients with clinical bleeding difficulties, we performed a retrospective survey of coagulation studies on 569 individuals referred to the University of Manitoba coagulation laboratory because they, or a closely related family member, showed clinical evidence of a bleeding disorder. There was a highly significant (p less than 0.001) negative correlation between the bleeding time and each of the following parameters: the platelet count; the hematocrit; the percent aggregation to collagen, epinephrine, ADP, and arachidonic acid; and the logarithm of von Willebrand factor antigen and a measure of its activity (ristocetin cofactor). A significant and independent inverse relationship between the length of the bleeding time and the extent of platelet adhesion to glass beads, patient age, and prothrombin consumption were also observed. Multivariate analysis of the ability of all parameters to predict the bleeding time showed an r2 of only 0.33. Bleeding time thromboxane B2, in a second smaller study of 70 patients, showed a negative correlation with the length of the bleeding time (p = 0.0001), and, when used together with the above parameters, significantly enhanced the ability to predict the length of the bleeding time (r2 = 0.55). Defects in platelet function, as measured in vitro, and significant enough to have an effect on the bleeding time, occurred with greater frequency than defects in von Willebrand factor in the Manitoba patients evaluated.

Contractile activity of neonatal platelets

Platelet contractile activity was evaluated by observation of tension development during isometric contraction of platelet-fibrin clots. Cylindrical clots were made with platelet-rich plasma obtained from cord blood or from adult controls. These clots were allowed to contract isometrically at 37 degrees C while attached to a transducer to record tension development. The rate of tension development was dependent on platelet concentration but was equivalent for neonatal and adult platelet clots. Although abnormalities in neonatal platelet aggregation and secretion have been well documented the platelet functions required for clot contraction such as fibrin binding and actin-myosin interaction appear to be intact in neonatal platelets.

Differential effects of spermine on aggregation, inositol phosphate formation and protein phosphorylation in human platelets in response to thrombin, arachidonic acid and lysophosphatidic acid

Platelet aggregation stimulated by thrombin, arachidonic acid or lysophosphatidic acid is associated with rapid phosphorylation of two platelet proteins, myosin light chain and a 47 kDa protein. The polyamine, spermine, inhibited platelet aggregation stimulated by all three agents. Spermine inhibited thrombin-stimulated phosphorylation of myosin light chain and the 47 kDa proteins as well as thrombin-induced production of the inositol phosphates and phosphatidic acid. In contrast, spermine did not inhibit phosphorylation of either protein or the formation of inositol phosphates and phosphatidic acid in response to arachidonic acid or lysophosphatidic acid. Although spermine has been demonstrated to inhibit both phosphatidylinositol-specific phospholipase C and calcium-dependent protein kinases in cell free systems, these results suggest that, in the intact platelet, spermine does not directly inhibit these enzymes. Inhibition of aggregation stimulated by arachidonic acid and lysophosphatidic acid is secondary to interference with platelet-platelet interaction but not with platelet activation. In contrast, spermine inhibits thrombin-induced platelet activation. This thrombin-specific inhibition may be related to interference with the binding of thrombin to its receptor or to its catalytic substrate on the cell surface.

Activation of permeabilized platelets by inositol-1,4,5-trisphosphate

The effect of inositol 1,4,5-trisphosphate (IP3) was studied using human platelets permeabilized with saponin and suspended in a high potassium, Ca2+-free buffer containing 40 microM EGTA and 1.2 mM magnesium. Under these conditions IP3 stimulated aggregation at a concentration of 0.5 microM with maximum aggregation at 5.0 microM. Aggregation was associated with phosphorylation of myosin light chain and a 47,000 dalton protein, and with a change in platelet shape including granule centralization and pseudopod formation similar to changes seen when cytoplasmic calcium is raised by other means. IP3 stimulated [14C]-serotonin release from platelet dense granules, [14C]-arachidonic acid release from platelet phospholipids and production of thromboxane B2. Preincubation of platelets with aspirin which blocked thromboxane formation also inhibited protein phosphorylation, serotonin secretion and partially inhibited aggregation. These results support the concept that IP3 is a major intracellular messenger in platelets and suggests that its effects are mediated both through Ca2+ flux and thromboxane formation.

Platelet protein phosphorylation

As can be seen from this review, protein phosphorylation appears involved in both positive and negative regulation of platelets. To date, good evidence has been presented for the involvement of protein phosphorylation in the regulation of granule centralization (i.e. myosin light chain phosphorylation). It is probable that protein phosphorylation may also be involved in granule labilization, pseudopod formation and ATP synthesis. Protein phosphorylation in association with platelet activation appears mediated through calcium flux, in the case of myosin light chain phosphorylation, and through diglyceride or other substances in the case of 47P phosphorylation. A summary scheme is shown in Figure 1.

Synovial sarcoma in childhood

The clinical and radiologic findings in seven children with synovial sarcoma are described. The five boys and two girls had a mean age at presentation of 4.4 years. All seven had the lesion situated in an extremity. Plain radiographs in four revealed the presence of a soft-tissue mass with no calcification or bone and joint involvement. In two patients studied with computed tomography (CT), the primary lesions had peripheral irregular areas of enhancement with central areas of poor enhancement, reflecting the necrotic, cystic, and hemorrhagic changes found in the centers of these tumors. Although the exact margins of these lesions were difficult to define accurately even with intravenous contrast enhancement, CT is still recommended as the best imaging method for assessing the local extent of the primary tumor and is a useful tool in the planning of appropriate therapy as well as the gauging of tumor response to ongoing treatment.

Traumatic aneurysm of the popliteal artery due to an osteochondroma of the femur

The authors report the case of a 51-year-old man who had a false aneurysm of the popliteal artery caused by erosion by an adjacent osteochrondroma of the femur. The osteochondroma was removed and the artery repaired by end-to-end anastomosis. Seventeen similar cases, which have been recorded in the past 15 years, are reviewed. These reports emphasize the importance of surgical repair to avoid permanent ischemic damage to the leg and foot.