Jose Martinez

Platelet dysfunction in uremia. Multifaceted defect partially corrected by dialysis

In an attempt to elucidate the nature of the bleeding tendency in uremia, some in vitro functions of platelets from eight patients undergoing long-term hemodialysis were studied. None of the patients had diabetes. All had bleeding times longer than eight minutes. Threshold aggregating concentrations for collagen, adenosine diphosphate, and epinephrine, when used singly or in pairs, were two to three times higher than normal in platelet-rich plasmas from these patients. In contrast, those for arachidonic acid and U-46619, a cyclic endoperoxide/thromboxane A2 analogue, were within the normal ranges. Thromboxane B2 formation was normal in response to arachidonic acid (0.2 to 1 mM), whereas it was decreased by 30 to 50 percent in response to thrombin (0.5 to 10 units/ml), collagen (0.5 to 10 micrograms/ml), and the combination of collagen with adenosine diphosphate or epinephrine. There was a partial (about 35 percent) reduction of the platelet granular content of adenosine diphosphate. Secretion of adenosine triphosphate by 5 units/ml of thrombin was 25 to 50 percent less than in normal subjects. Thus, there was a storage pool defect as well. Similar but less severe defects were found in platelets from uremic patients who had never undergone hemodialysis. Partial correction of aggregation and thromboxane B2 formation was seen after dialysis, although platelet adenosine diphosphate content did not increase. It is concluded that the platelet dysfunction in uremia is multifaceted. There appears to be an aggregation and secretion defect related to impaired arachidonic acid release from platelet phospholipids as well as a storage pool defect. The first is improved with dialysis; the second is not.

Thymosin beta4 enhances endothelial cell differentiation and angiogenesis.

When human umbilical vein endothelial cells (HUVEC) differentiate into capillary-like tubes, there is a five-fold upregulation of the mRNA for thymosin β4 (Tβ4) (Grant et al. J Cell Sci 1995; 108: 3685–94 [1]) and this endogenous expression plays an important role in endothelial cell attachment to and spreading on matrix components. We now show that exogenous addition of thymosin β4 (in the ng–μg range) to HUVEC in culture can induce several biological responses. These responses include increased tube formation in vitro. Additionally, exogenous thymosin β4 enhances vascular sprouting in the coronary artery ring angiogenesis assay. Measurements of these vascular sprouts show a doubling of the vessel area (via increased branching) with as little as 100 ng of synthetic thymosin β4. These processes appear to involve the binding of thymosin β4 to an unknown cell surface receptor and internalization of the protein. This cell surface-binding appears not to be mediated through the thymosin β4-actin binding domain LKTET. An increase in thymosin β4 cytoplasmic staining in HUVEC exposed 10 μg of the peptide appears to occur without increased mRNA translation. In summary Tβ4 induces an increase in cell-matrix attachment, proliferation, tube formation, internalization of the peptide and rearrangement of the actin cytoskeleton. The data now defines both an autocrine and paracrine role for thymosin β4 in vessel formation.

Endothelial Cell VE-cadherin Functions as a Receptor for the β15–42 Sequence of Fibrin

The contact of fibrin with the apical surface of human umbilical vein endothelial cells (HUVEC) can induce capillary tube formation via the interaction of fibrin β15–42 with a putative cell receptor (Chalupowicz, D. G., Chowdhury, Z. A., Bach, T. L., Barsigian, C., and Martinez, J. (1995) J. Cell Biol. 130, 207–215). To characterize this interaction, we studied the binding of the thrombin-cleaved N-terminal disulfide knot of fibrin (NDSK II), a dimeric fragment with exposed β15–42, to HUVEC in three separate assay systems. Time-course binding of125I-NDSK II to HUVEC monolayers or suspensions revealed that binding was specific at 50–60%, as determined by the addition of unlabeled NDSK II. Specific binding of 125I-NDSK II to HUVEC was 70% reversible by dilution or by competition, and was found to be divalent cation-independent. Binding plateaued after 10 min at a saturation of 15–20 nm. Scatchard analysis using the LIGAND computer program defined a single population of receptors with aK D of 7.7 ± 1.6 nm and approximately 21,000 ± 7000 binding sites/cell. N-terminal disulfide knot derivatives in which β15–42 was absent (NDSK 325) or unexposed (NDSK, NDSK I) did not show specific binding. Specific binding of 125I-NDSK II could not be inhibited by RGDS or by antibodies to the αvβ3 or β1 integrins, PECAM-1, ICAM-1, or N-cadherin. In contrast, a synthetic β15–42/ovalbumin conjugate inhibited total125I-NDSK II binding by 47 ± 19% (corresponding to 95% of specific 125I-NDSK II bound) and a monoclonal antibody to vascular endothelial cadherin (VE-cadherin) inhibited binding by 35 ± 8% (corresponding to 70% of specific125I-NDSK II bound). Another assay was based on the capture of cadherins from HUVEC lysates by a polyclonal pan-cadherin antibody immobilized on plastic dishes. Binding of NDSK II to the captured cadherins was 89 ± 5% specific, while specific binding of NDSK 325 and NDSK was negligible. An immortalized line of human adipose-derived microvascular endothelial cells, which express N-cadherin but not VE-cadherin, demonstrated no specific binding of NDSK II by the capture assay. These data define a novel interaction of fibrin with VE-cadherin, which is mediated by the fibrin N-terminal β15–42 sequence, and may contribute to the mechanism through which fibrin induces angiogenesis.

Abnormal sialic acid content of the dysfibrinogenemia associated with liver disease.

To evaluate the possibility that the carbohydrate composition of fibrinogen may be altered in the dysfibrinogenemia associated with liver disease, we studied the sialic acid content of purified fibrinogen from 12 patients with liver disease and its relationship to the prolongation of the thrombin time. Purified fibrinogen showed that Aalpha-, Bbeta-, and gamma-chains when reduced and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and exhibited prolongation of the thrombin time similar to that of the plasma from which it was derived. Sialic acid content of the purified fibrinogen ranged from 12.7 to 71.4% higher in patient fibrinogens when compared to normal controls. A progressive delay in thrombin time was associated with increasing sialic acid content of the patient fibrinogen. Enzymatic removal of sialic acid from four of the abnormal fibrinogens resulted in a shortening of their thrombin times to the range of the desialylated normal control. Periodic acid-Schiff reagent stained only the Bbeta- and gamma-chains of the reduced patient fibrinogens after sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggesting that the excess sialic acid is located on these two chains. These studies demonstrate a biochemical alteration of the functionally abnormal fibrinogen found in some patients with liver disease, and indicate that the excess sialic acid plays an important role in the functional defect of this protein.

Dysfibrinogenemia Associated with Liver Disease

To test the possibility that a functionally abnormal fibrinogen may exist in some patients with liver disease, we studied the plasma and purified fibrinogens of five patients whose plasma thrombin times were prolonged at least 40% over normal controls. In no patient was there evidence of disseminated intravascular coagulation and/or fibrinolysis. No abnormalities were detected by immunoelectrophoresis of plasmas or purified fibrinogens. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of reduced patient fibrinogens showed normal mobility and amount of Aalpha, Bbeta, and gamma chains. Alkaline polyacrylamide gel electrophoresis and gradient elution, DEAE-cellulose chromatography of admixtures of radio-iodinated patient (125)I-fibrinogen and normal (131)I-fibrinogen showed identical mobility in the gel and simultaneous elution from the column, respectively. Thrombin and Reptilase (Abbott Scientific Products Div., Abbott Laboratories, South Pasadena, Calif.) times of purified patient fibrinogens were prolonged, and calcium ions improved but did not completely correct these defects. Increasing amounts of thrombin progressively shortened the clotting times of patient fibrinogens but not to the level of normal. Addition of equal amounts of patient fibrinogen to normal fibrinogen resulted in a prolongation of the thrombin time of the normal protein. Thrombin-induced fibrinopeptide release was normal. Fibrin monomers prepared from patient plasmas and purified fibrinogens demonstrated impaired aggregation at low (0.12) and high (0.24) ionic strength. These studies demonstrate that some patients with liver disease and prolonged plasma thrombin times have a dysfibrinogenemia functionally characterized by an abnormality of fibrin monomer polymerization.

Pulmonary hypertension in patients with myelofibrosis secondary to myeloproliferative diseases

We examined the clinical characteristics of six patients with myelofibrosis secondary to myeloproliferative diseases whose clinical courses were complicated by pulmonary hypertension to determine possible causal links between the two disorders. Six patients (four male, two female), with diagnoses of myeloproliferative disease, myelofibrosis (one with polycythemia vera, three with agnogenic myeloid metaplasia, one with unclassified myeloproliferative syndrome, one with essential thrombocytosis), and pulmonary hypertension are presented. Measurement of the pulmonary artery pressure was performed by Doppler echocardiography in all patients and by right sided heart catheterization in four patients. The range of resting pulmonary artery systolic pressure was 35 to 47 mmHg above the mean right atrium by echocardiography. One patient had autopsy evidence of pulmonary myeloid metaplasia and interstitial fibrosis; another had acute leukemic infiltration of the lung parenchyma. All patients had thrombocytosis; symptomatology in one patient with marked thrombocytosis improved with plateletpheresis. Two patients suffered systemic thrombosis. All patients had severe hepatomegaly. Two patients had evidence of left ventricular dysfunction. The interval between the development of dyspnea and death was less than seven months in five of the patients. A causal link between pulmonary hypertension and myelofibrosis secondary to myeloproliferative diseases is suggested for each patient. Hematopoietic infiltration of the pulmonary parenchyma, portal hypertension, thrombocytosis, hypercoagulability, and left ventricular failure may account in part for the development of pulmonary hypertension in these patients. Patients with myelofibrosis and dyspnea should have Doppler echocardiography to evaluate pulmonary artery pressures. Am. J. Hematol. 60:130–135, 1999.

Interaction of Fibrin with VE-Cadherin

Abstract: The conversion of fibrinogen into fibrin and the association of fibrin(ogen) with activated platelets play a fundamental role in hemostasis because their interaction with the injured vessel prevents blood extravasation. Platelet aggregates and fibrin also participate in the occlusion of the vascular lumen in pathological conditions. Fibrin II also promotes the formation of new blood vessels, for example, during wound healing and tumor growth. Using an in vitro assay, we have studied the mechanism by which fibrin II induces formation of capillaries. Generation of fibrin II on top of an endothelial cell monolayer rapidly rearranged the ECs into a capillary network. In contrast, neither fibrin I nor fibrin 325 induced these morphogenetic changes, indicating that exposure of the N‐terminal peptide β15–42 is involved in this process. Binding studies, using the N‐terminal fragment of fibrin (NDSK II), showed that NDSK II binds to EC with high affinity, but neither NDSK nor NDSK325 bound specifically. Binding of NDSK II to endothelial cells was blocked with an antibody to VE‐cadherin. Direct association of NDSK II and VE‐cadherin was also demonstrated in a VE‐cadherin antibody capture assay. NDSK II bound specifically with the captured VE‐cadherin but NDSK or NDSK 325 did not associate with VE‐cadherin. Moreover, fibrin II associated with EC VE‐cadherin and this interaction triggered the formation of capillary‐like structures. A better understanding of the cellular responses to fibrin, identification of the fibrin binding site within VE‐cadherin and the intracellular signaling that follows this interaction, could yield important information that may translate into better control of the angiogenic process.

Immunohistochemical demonstration of tissue transglutaminase in amyloid plaques

Abstract The brain of Alzheimer’s disease patients contains deposits of the 39–42-amino acid (∼ 4 kDa) amyloid β-peptide, which is derived from the β-amyloid precursor protein. These pathological deposits have been shown to consist in part of insoluble 8- and 16-kDa aggregates of the amyloid β-peptide. This report confirms that the amyloid β-peptide is a substrate for tissue transglutaminase (TGase) and demonstrates that human brain preparations from Alzheimer’s disease patients and control patients form cross-linked dimers from added iodinated amyloid β-peptide. Immunohistochemical staining for TGase revealed its presence in tissue sections and isolated amyloid plaque cores obtained from brains of patients diagnosed as having Alzheimer’s disease. These results provide evidence that the previously described insoluble amyloid deposits in Alzheimer’s disease may involve TGase-mediated cross-linked amyloid β-peptide polymers, and suggest a potential role for TGase in the pathogenesis of this disease.

The hyperviscosity syndrome, polysynovitis, polymyositis and an unusual 13S serum IgG component

A patient is described in whom chronic polysynovitis, polymyositis and the hyperviscosity syndrome developed, and whose serum contained an unusual IgG that circulated mainly as a polyclonal 13S component, with rheumatoid factor-like activity. The 13S serum component, which at times represented more than 40 per cent of the serum total protein, was the major factor responsible for serum hyperviscosity. A striking correlation was observed among the following factors: intensity of the synovitis, intensity of the myositis, the concentration of serum IgG and 13S serum component concentration. Each seemed to be decreased by the administration of prednisone. The possible significance of these various interrelationships is discussed.

Normalization of plasma factor X levels in amyloidosis after plasma exchange.

Some patients with systemic light chain amyloidosis develop bleeding complications that can be caused by vascular infiltration with amyloid or by alterations of the coagulation or fibrinolytic systems. Factor X deficiency is the most common cause of bleeding manifestations, although deficiencies of other clotting factors, a disruption in the conversion of fibrinogen to fibrin, and circulating heparin‐like anticoagulants have also been reported. Deficiency of factor X is a well‐recognized cause of bleeding manifestations in patients with light chain amyloidosis. This acquired disorder appears to be secondary to adsorption of factor X to the amyloid fibrils. Previous studies have shown that infusion of plasma into patients with acquired factor X deficiency and amyloidosis induces a transitory improvement of the coagulation tests. However, there is a rapid return to pretransfusion levels. In this manuscript we report the clinical application of plasma exchange in the management of a patient with systemic light chain amyloidosis with acquired factor X deficiency. Am. J. Hematol. 54:68–71, 1997