Perioperative evaluation of primary hemostasis in patients undergoing mitral valve repair.

INTRODUCTION: No data exist on the prevalence of primary hemostatic defects and acquired von Willebrand disease in mitral valve prolapse with severe regurgitation. METHODS: Primary hemostasis was evaluated by PFA-100, von Willebrand Factor Antigen (vWF:Ag) and Ristocetin cofactor (vWF:RiCof) assays in a prospective observational trial. Sixty-five consecutive patients with mitral regurgitation (study group) or aortic stenosis (control group) who were operated for mitral valve repair or aortic valve replacement were enrolled in the study. RESULTS: There were no differences in Closure Time in the two groups at all time points. The concentration of plasma vWF: Ag was within normal limits in all patients preoperatively; after surgery, a significant increase was observed in both groups from baseline (199 +/- 144 mcg/dL vs. 295 +/-141 mcg/dL in the study group, p=0.002; 243 +/- 141 mcg/dLl vs 338 +/- 154 mcg/dL in the control group, p=0.009). The ratio of vWF:RiCof to vWF:Ag was slightly decreased preoperatively in both groups (ratio= 0.91) and showed a marked increase in the postoperative period (ratio=0.22) as, probably, new hemostatically effective large multimeric forms of vWF were released. CONCLUSIONS: Patients who present for surgery with a valvular pathology with high shear stress have some degree of primary hemostasis defect; nevertheless, the potent stimulus of surgery and the correction of the underlying disease allow quick restoration of vWF activity and normalization of PFA-100.

Changes in health and disease of the metalloprotease that cleaves von Willebrand factor.

Congenital or immunomediated deficiencies of the metalloprotease that cleaves physiologically von Willebrand factor (vWF) reduce or abolish the degradation of ultralarge vWF multimers that cause the formation of intravascular platelet thrombi in patients with thrombotic thrombocytopenic purpura (TTP). There is little knowledge on the behavior of the protease in other physiological and pathologic conditions. Such knowledge is important to evaluate the specificity of low protease plasma levels in the diagnosis of TTP. Using an enzyme immunoassay, the protease was measured in 177 control subjects of different ages, in 26 full-term newborns, and in 69 women during normal pregnancy. Because TTP is often associated with multiorgan involvement and acute phase reactions, clinical models of these pathologic conditions were also investigated, including decompensated liver cirrhosis (n = 42), chronic uremia (n = 63), acute inflammatory states (n = 15), and the preoperative and postoperative states (n = 24). Protease levels were lower in healthy persons older than 65 than in younger persons. They were low in newborns but became normal within 6 months, and they were lower in the last 2 trimesters of pregnancy than in the first. Protease levels were also low in patients with cirrhosis, uremia, and acute inflammation, and they fell in the postoperative period. There was an inverse relation between low protease and high plasma levels of vWF antigen and collagen-binding activity. In conclusion, low plasma levels of the vWF cleaving protease are not a specific beacon of TTP because the protease is also low in several physiological and pathologic conditions.

Proteolysis of von Willebrand factor and shear stress-induced platelet aggregation in patients with aortic valve stenosis.

BACKGROUND: Excessive bleeding may complicate congenital cardiac defects. To explain the pathogenesis of this abnormality, we evaluated selected parameters of primary hemostasis in patients with aortic valve stenosis before and after corrective surgery. METHODS AND RESULTS: We examined shear-induced platelet aggregation with the filter aggregometer test and von Willebrand factor (vWF) structure by evaluating the multimeric distribution and extent of subunit proteolysis. The platelet count was reduced before corrective surgery, and shear-induced platelet aggregation was impaired. Moreover, vWF multimers of higher molecular mass were decreased, and proteolytic subunit fragments were increased. After correction of the cardiac defect, all of these parameters returned to normal. CONCLUSIONS: Alterations of vWF and platelet function may contribute to the bleeding diathesis in patients with aortic valve stenosis. Improvement after corrective surgery suggests that the passage of blood through a stenosed aortic valve may result in shear forces that induce vWF interaction with platelets in the circulation and, in turn, trigger platelet clearance, vWF degradation, and the impairment of primary hemostasis.

Heightened proteolysis of the von Willebrand factor subunit in patients with von Willebrand disease hemizygous or homozygous for the C2362F mutation.

We studied the proteolytic pattern of the mutant von Willebrand factor (VWF) in four patients with von Willebrand disease (VWD) who were either homozygous or hemizygous for the mutation C2362F. A significant decrease in the native fragment of 225 kDa was evident in all the patients, together with a marked increase in the 176 and 140 kDa fragments, a pattern usually observed in type 2A VWD. The proteolytic pattern measured in four heterozygotes for C2362F was within the normal range, suggesting that the mutant VWF C2362F present in the plasma of these patients may be protected from proteolysis by normal VWF.

Transfusion requirements are correlated with the degree of proteolysis of von Willebrand factor during orthotopic liver transplantation.

During orthotopic liver transplantation (OLT) excessive bleeding is the main cause of death and graft failure. The acute bleeding tendency that accompanies OLT, particularly during the anhepatic period and after reperfusion of the graft, is due to the depletion or functional abnormalities of several hemostasis components caused by the enhanced activity of enzymes such as plasmin, trypsin and leukocyte proteases. We surmised that enhanced proteolysis might also cause abnormalities of von Willebrand factor (vWF), and that these abnormalities are implicated in the bleeding tendency that develops during OLT. Therefore, the pattern of vWF proteolysis was studied with 16 patients with chronic liver disease, in serial blood samples obtained before OLT, during the anhepatic stage, after graft reperfusion and at the end of the surgical procedure. vWF became markedly degraded during the anhepatic and reperfusion stages, as shown by the partial loss of high molecular weight multimers, the relative decrease of the intact 225 kD subunit and the increase of the native proteolytic fragments of 176 and 140 kD. Novel proteolytic fragments also became detectable. Using monoclonal antibody epitope mapping, it could be demonstrated that some of the proteolytic fragments corresponded in apparent molecular mass to those produced in vitro by incubating purified vWF with plasmin or elastase, but other fragments could not be attributed to these proteases. During the anhepatic and reperfusion stages there was a significant correlation between the degree of vWF degradation and the total amount of blood components transfused to replace blood losses. To evaluate whether or not vWF degradation could be controlled by the administration of a broad-spectrum protease inhibitor such as aprotinin, 5 patients were given a bolus dose of 500,000 U before surgery followed by 100,000 U/h during surgery, 5 were given a 2,000,000 U bolus followed by 500,000 U/h, and no aprotinin was given to the remaining 6 patients. There were no differences in the patterns or degrees of vWF degradation between patients treated with aprotinin or not. In conclusion, there is a marked degradation of a key hemostasis protein during OLT. These alterations may be of clinical significance, because they are correlated with the transfusion requirements.

Systemic clotting activation by low-grade endotoxaemia in liver cirrhosis: a potential role for endothelial procoagulant activation.

BACKGROUND: The pathophysiologic mechanism underlying the association between endotoxaemia and clotting activation in liver cirrhosis is still to be explained. AIMS: To investigate the relationship between endotoxaemia, endothelial perturbation and clotting system activation in liver cirrhosis patients. PATIENTS: The study was carried out in 30 consecutive patients (17 males, 13 females, age range 42 to 71 years) with liver cirrhosis. METHODS: Prothrombin fragment F1 + 2, endotoxaemia, von Willebrand factor and ristocetin cofactor activity were studied in all patients. Von Willebrand factor antigen release and tissue factor expression were also evaluated in cultured endothelial cells incubated with low endotoxin concentrations (125-500 pg/ml). RESULTS: Thirteen (43%) out of 30 liver cirrhosis patients showing von Willebrand factor antigen levels > 157 IU/dl (mean +/- 2SD of controls) were considered to have signs of endothelial perturbation; they had more severe liver failure (p = 0.0001), higher ristocetin cofactor activity (p = 0.0001), endotoxin (p = 0.0001) and prothrombin fragment F1 + 2 (p = 0.0001) plasma values than liver cirrhosis with normal von Willebrand factor antigen. A strong correlation (r = 0.97; p = 0.0001) was found between prothrombin fragment F1 + 2 and von Willebrand factor antigen. In in vitro experiments endotoxin induced a concentration-dependent release of von Willebrand factor antigen (p = 0.0001) and expression of tissue factor activity (p = 0.0001) and antigen (p = 0.0001) from cultured endothelial cells. CONCLUSIONS: This study suggests that the endothelial procoagulant activation induced by low-grade endotoxaemia may represent a trigger for systemic clotting activation in liver cirrhosis patients.

High plasma levels of von Willebrand factor as a marker of endothelial perturbation in cirrhosis: relationship to endotoxemia.

The aim of this study was to evaluate whether there is endothelial dysfunction in patients with cirrhosis and to detect the mechanism that may account for it. We measured plasma levels of von Willebrand factor (vWF), a marker of endothelial perturbation, and endotoxin, which releases vWF from endothelial cells in vitro, in 32 patients (18 men, 14 women, aged 39-70 years) with cirrhosis classified as mild (class A, n = 10), moderate (class B, n = 16), or severe (class C, n = 6) according to Child-Pugh's classification. vWF antigen (P < .0001) and endotoxemia (P < .0001) progressively increased from A to class C; but the increase of vWF antigen was not strictly related to liver failure, as shown by the lack of correlation between vWF and several indexes of liver protein synthesis. Analysis of the vWF subunit showed no sign of proteolytic fragmentation of the molecule. Multimeric analysis indicated intact vWF multimeric structure. In all patients, there was a strong correlation between vWF antigen and endotoxemia (rho = .92; P = .0001). In 20 selected patients, vWF antigen and endotoxemia were measured before and after 7 days of standard therapy (n = 10) or standard therapy plus nonabsorbable antibiotics. There was a significant decrease of vWF antigen (P < .02) concomitantly with the decrease of endotoxemia (P < .006) in patients taking nonabsorbable antibiotics. Human umbilical vein endothelial cells incubated in vitro with 125 to 500 pg/mL endotoxin released vWF antigen into the medium dose dependently. These results demonstrate that there is endothelial perturbation in cirrhosis and that endotoxemia may play a key role in its occurrence.

Analysis of Arg834Gln and Val902Glu type 2A von Willebrand disease mutations: studies with recombinant von Willebrand factor and correlation with patient characteristics.

Type 2A von Willebrand disease (vWD), the most common qualitative form of vWD, is characterized by a relative decrease in circulating intermediate and high molecular weight (HMW) multimers. We studied the biosynthesis of recombinant von Willebrand factor (vWF) containing each of two type 2A vWD mutations previously reported by us, Arg834Gln and Val902Glu. The structure of recombinant Arg834Gln vWF within transfected COS-7 cells and the secretion of HMW multimers were similar to wild type vWF. The normal transport and secretion of Arg834Gln vWF, categorizes it as a group II type 2A mutation. In contrast, the Val90-2Glu mutation resulted in intracellular proteolysis of vWF with the generation of a 176-kD fragment and retention of vWF between the endoplasmic reticulum and the Golgi complex. Moreover, the 176-kD fragment was also increased in plasma from patients with the Val902Glu mutation. Significantly impaired secretion and intracellular proteolysis of Val902Glu vWF categorizes a new sub-group of type 2A mutations. The intracellular proteolysis of vWF Val902Glu explains the lack of response to 1-deamino 8-D-arginine vasopressin (DDAVP) in patients who carry the mutation.

Proteolysis of von Willebrand factor is decreased in acute promyelocytic leukaemia by treatment with all-trans-retinoic acid.

Plasma von Willebrand factor (VWF) was investigated in five patients with acute promyelocytic leukaemia (APL) before and after administration of the differentiating agent all-trans-retinoic acid (ATRA). The purpose of this study was to see how the proteolytic state associated with APL affects VWF structure and function and whether ATRA reverses any abnormality. At the onset of APL, multimeric analysis of plasma VWF revealed a lack of the largest multimers. After ATRA, there was a progressive correction of the multimeric pattern in all cases, with transient appearance of ultralarge multimers in two cases. Proteolysis was investigated with immunopurified and reduced VWF from each patient's plasma. This was electrophoresed and probed with two monoclonal antibodies that identify the 225 kD native subunit and the three native fragments of 189, 176 and 140 kD and differentiate novel proteolytic fragments produced by different proteinases. At the onset of APL, the 225 kD native subunit was relatively decreased, with the appearance of an array of novel VWF proteolytic fragments, ranging in size from <140 to <225 kD. These novel fragments observed in patients were similar to those produced in vitro by digestion of purified VWF with plasmin or elastase. After ATRA therapy, proteolysis diminished progressively in parallel with the improvement of other haemostatic measurements, but persisted to some extent. We conclude that VWF proteolysis in APL is produced by plasmin and elastase. Changes of VWF structure and function might adversely affect haemostasis in APL. Therefore, improvement of VWF after ATRA administration might explain in part the effectiveness of this drug in reducing haemorrhagic complications.

Platelet von Willebrand factor abnormalities in myeloproliferative syndromes.

Plasma and platelet von Willebrand factor (vWF) measurements, multimeric pattern and subunit composition of plasma vWF were obtained in 29 consecutive patients with chronic myeloproliferative syndromes. In the 8 patients with chronic myelogenous leukemia (CML), plasma vWF was significantly higher than in the 11 patients with essential thrombocythemia (ET) and in the 10 patients with polycythemia vera (PV). The RiCof/vWF:Ag ratio was low in all these groups of patients (mean 0.64 +/- 0.1, 0.66 +/- 0.2, and 0.61 +/- 0.2; normal 0.97 +/- 0.2). Bleeding time was prolonged (> 7.5 min) in 1/8 CML patients, 1/10 with PV, and 3/11 with ET. Plasma vWF multimers showed a minor loss of the largest multimers in 3/8 patients with CML, 4/10 with PV, and a more severe reduction in 9/11 ET patients. The latter pattern correlated with an abnormal proteolysis of vWF, expressed by a major increase of the 140-Kd fragment and decrease of the intact 225-Kd subunit in ET patients, whereas the 176-Kd fragment was significantly increased in all the subgroups of patients. Platelet vWF was significantly higher in CML patients in comparison to ET and normal controls. However, minor losses of the larger multimers were evident in all the subsets of patients. In ET patients also the intermediate forms were lacking in platelets, accompanied by a significant decrease of platelet RiCof. This abnormality was significantly correlated with the occurrence of bleeding symptoms in PV and ET patients (P = 0.007; Fisher's exact test). In conclusion, plasma and platelet vWF abnormalities are common findings in myeloproliferative syndromes and are more severe in ET. The more pronounced platelet vWF abnormalities in ET may reflect the more frequent bleeding symptoms observed in this disorder.

Characterization of two cases of acquired transitory von Willebrand syndrome with ciprofloxacin: evidence for heightened proteolysis of von Willebrand factor.

We characterized the cause of two cases of transitory acquired von Willebrand syndrome associated with the administration of ciprofloxacin. Purified Ig from the two patients did not inhibit Ristocetin Cofactor activity or binding to collagen of normal plasma, ruling out the possibility of an inhibitor. The analysis of multimeric pattern of plasma von Willebrand Factor (vWF) showed the lack of larger multimers in both patients, with a relative decrease of all the remaining forms in the first patient. The subunit composition of plasma vWF showed a marked reduction of the native 225 Kd subunit (31.9% and 32.9%; normal range 74-86%) and an increased proportion of the 189, 176, and 140 Kd fragments. These abnormalities disappeared during the follow-up, without any specific therapy. In conclusion, a common pathophysiological basis is demonstrated in both patients, with a heightened proteolysis of plasma vWF by an unknown mechanism.

Factor VIII:C increases after desmopressin in a subgroup of patients with autosomal recessive severe von Willebrand disease.

Patients with severe von Willebrand disease (vWD) usually show no increase of factor VIII/von Willebrand factor (VIII/vWF) after desmopressin (DDAVP) infusion and the bleeding time (BT) remains markedly prolonged. We have tested the biological responsiveness to DDAVP in six patients, belonging to six different families, with phenotypic evidence for severe vWD. Baseline VIII:C ranged from 12 to 32IU/dl, ristocetin cofactor activity (RiCof) was unmeasurable in all the patients, vWF antigen (vWF:Ag) ranged from 0.5 to 3.5 IU/dl, and in all patients the BT was longer than 30 min. No measurable vWF was present in patient's platelets, and plasma and platelet vWF multimers were virtually absent. An autosomal recessive pattern of inheritance was evident in all the propositi. After DDAVP infusion, there was no BT shortening. In four patients, VIII:C increased post-infusion and in three patients levels greater than 50 IU/dl were attained. RiCof reached a maximum of 11 IU/dl and vWF:Ag 9 IU/dl. In one of these four patients, DDAVP allowed a safe dental extraction, without resorting to blood products. In the remaining two patients no VIII/vWF changes were observed after DDAVP. In conclusion, a subgroup of patients with severe vWD shows an increase of VIII:C after DDAVP. A test infusion with this agent is advisable in patients with severe vWD before considering treatment with VIII/vWF concentrates.

Proteolysis of von Willebrand factor in therapeutic plasma concentrates.

Therapeutic plasma concentrates containing vo Willebrand factor (vWF) lack the largest, most hemostatically active multimers. To evaluate whether this abnormality results from proteolysis during manufacturing, we have analyzed the subunit structure of vWF in several commercial products and found a marked reduction in the relative content of intact 225-kD subunit, paralleled by an increase in the proteolytic fragments normally present in plasma, particularly that of 176 kD. There was no heightened vWF fragmentation in blood-bank cryoprecipitate prepared from platelet-poor, single-donor plasma; in contrast, there was a marked degree of fragmentation in cryoprecipitate prepared from pooled plasmapheresis plasma representing the starting fraction for the production of commercial concentrates. In cryoprecipitate prepared experimentally from plasma containing varying numbers of platelets, the degradation of vWF was proportional to the platelet count, but was greatly diminished by adding protease inhibitors to the plasma. On the basis of these findings, we postulate that the loss of the largest vWF multimers in commercial products results from the use of poorly centrifuged plasmapheresis plasma containing an excessive number of residual platelets and leukocytes. These cells, lysing when plasma is frozen and thawed for the preparation of cryoprecipitate, may liberate proteolytic enzymes that cleave the vWF subunit and contribute to the degradation of the largest multimers. Our results should help devise new approaches for the preparation of more effective concentrates for the treatment of von Willebrand disease.

Multimeric pattern of plasma and platelet von Willebrand factor is normal in uremic patients.

Several studies have reported increased von Willebrand factor (vWF) levels in plasma of uremic patients, with a normal multimeric pattern. Two recent studies, however, have shown a reduction of the larger multimers of plasma vWF and one has also found low levels of platelet vWF in uremic patients with prolonged bleeding time (BT). We have measured plasma and platelet vWF and analyzed its multimeric pattern in 20 uremic patients, 11 with a prolonged BT and 9 with a normal BT. For Plasma vWF, no difference for vWF:Ag, RiCof, and ristocetin-induced platelet agglutination was found between the two groups with normal and prolonged BT. The multimeric pattern of plasma vWF, as evaluated by densitometric scanning of the electrophoretic gels, was normal in both groups. For platelet vWF, vWF:Ag and RiCof content was similar in the two groups. The multimeric pattern was indistinguishable from that of normal platelets. In conclusion, our study does not confirm the presence of a structural defect of plasma vWF and the reduction of platelet vWF content in uremia.

Desmopressin-induced thrombocytopenia in type I platelet discordant von Willebrand disease.

Thrombocytopenia after desmopressin (DDAVP) infusion is usually observed in patients with type IIB von Willebrand disease (vWD). No other subtypes of vWD with thrombocytopenia after DDAVP have been reported so far. We describe here the occurrence of thrombocytopenia after DDAVP in a 39 year old male and his son with phenotypic characteristics of type I vWD, "platelet discordant subtype." After DDAVP, the abnormal ristocetin cofactor/von Willebrand factor antigen ratio in plasma was not corrected and the bleeding time remained markedly prolonged. Platelet count dropped 30 min after DDAVP (from 279 to 96 x 10(3)/microL in the propositus and from 298 to 116 x 10(3)/microL in his affected son) and returned to normal at 60 min. Platelet clumping was evident on peripheral blood smears obtained after infusion. These cases indicate that after DDAVP thrombocytopenia can occur in vWD other than type IIB.

Degradation of von Willebrand factor in patients with acquired clinical conditions in which there is heightened proteolysis.

The behavior of plasma von Willebrand factor (vWF) in patients with acute leukemia (n = 5), decompensated cirrhosis (n = 10), and acute pancreatitis (n = 5) was investigated to evaluate whether the systemic proteolytic states associated with these diseases had affected the structure and function of the molecule. vWF antigen and, to a lesser degree, ristocetin cofactor activity in patient plasma were high. Multimeric analysis of plasma vWF revealed loss of high molecular weight multimers. The subunit composition and proteolytic pattern of vWF immunopurified from patient plasmas and reduced were studied by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis followed by transblotting and probing with monoclonal antibodies that distinguish cleavages caused by plasmin from those caused by other proteases. There was marked reduction of the relative concentration of the native vWF subunit of 225 Kd in all patient groups, indicating heightened cleavage of the protein. The concentrations of 189- and 140-Kd vWF fragments, normally present in plasma, were increased in cirrhosis and pancreatitis but not in leukemia. Novel fragments, ranging in size from less than 225 to approximately 120 Kd were present in leukemia and cirrhosis, including plasmin-generated fragments of 176 and 145 Kd. These data indicate that in clinical conditions in which there is heightened proteolysis vWF is degraded in vivo by plasmin and other proteases. Degraded vWF may be less effective than native vWF in supporting primary hemostasis, thereby being a cofactor in the multifactorial bleeding diathesis accompanying systemic proteolytic states.

A new variant of von Willebrand disease (type II I) with a normal degree of proteolytic cleavage of von Willebrand factor.

A variant of type II von Willebrand disease (vWd) is described in a young woman and her mother with severe lifelong bleeding histories. On electrophoresis with low-resolution agarose gels the plasma of the proband lacked large and intermediate-size multimers of von Willebrand factor (vWF) but the platelet multimeric structure was normal. On high-resolution gels, smaller multimers could be resolved into a broader central band and four satellite bands, which were much fainter than in normal plasma. In the proband plasma, the relative concentrations of proteolytic fragments of the vWF subunit were within the normal laboratory range. Since this variant of vWd appears to differ from those reported hitherto, the designation of type II I is proposed.