Increased plasma von Willebrand factor in the systemic inflammatory response syndrome is derived from generalized endothelial cell activation

Abstract

Objectives: Von Willebrand factor antigen (vWf) is an essential hemostatic protein. Increased plasma levels have been documented in patients suffering from the systemic inflammatory response syndrome (SIRS) and resulted presumably from endothelial cell damage specific to the site of injury. We hypothesize that increased plasma levels result from systemic endothelial cell activation and degranulation. Design: We compared immunohistochemical vWf staining in dermal biopsy specimens from patients with SIRS to healthy control subjects in the presence and absence of recombinant human tumor necrosis factor (rhTNF)-alpha. Also, we quantified plasma levels of vWf in these groups using a newly available antibody. Setting: A tertiary care surgical intensive care unit in a university teaching hospital. Subjects: Patients with SIRS and healthy controls. Interventions: Biopsies and blood samples were obtained from study groups. Measurements and Main Results: Decreased baseline vWf staining was noted in SIRS patients. The rhTNF-alpha caused a statistically significant decrease in vWf staining in control subjects but not in SIRS patients. Plasma vWf levels were increased an average of 11-fold in SIRS patients compared with control subjects. Conclusion: We postulate that the increased plasma levels of vWf and the decreased staining in the peripheral dermal plexus represent the generalized activation and degranulation of endothelium in vascular beds remote from the original inflammatory focus. (Crit Care Med 1998; 26:296-300) The systemic inflammatory response syndrome (SIRS) is the cumulative expression of host immune and metabolic responses to injury and infection. The pathogenesis of this syndrome is partially related to the elaboration of cytokines, aberrant immune cell function, and inadequate oxygen extraction and metabolism [1,2]. Recent investigations have implicated regional hypoperfusion and cytokine-induced activation of endothelial cells as central to these processes. Hypoperfusion leads to activation of platelets and leukocytes. When coupled with flow disturbances and a prothrombogenic endothelial surface, microvascular thrombosis and worsening tissue ischemia result [3,4]. These events culminate in whole-body inflammation, coagulopathy, and organ injury associated with SIRS. If persistent and overwhelming, the host enters the spiral of increasing organ dysfunction, eventually leading to death. Various cytokines, particularly tumor necrosis factor (TNF), have been have been closely linked as significant mediators in the pathogenesis of SIRS[5]. TNF was first identified by its ability to produce hemorrhagic necrosis of tumors [6] due to its prothrombogenic effects on vascular endothelium including upregulation of tissue factor, decreased fibrinolytic activity, and decreased thrombomodulin expression with a resultant decrease in generation of activated protein C [7-10]. Given the striking prothrombogenic capacity of TNF, its effects on von Willebrand factor (vWf) have been evaluated. The vWf is a macromolecular protein complex which plays a pivotal role in hemostasis, functions as a carrier protein for plasma factor VIII, and mediates platelet adhesion to collagen exposed by damaged endothelium and to other platelets [11]. The vWf is synthesized by vascular endothelial cells [12], platelets, and megakaryocytes [13]. Because of the extensive size of vWf, it is likely that the vascular endothelium is the major source of plasma vWf under physiologic and most pathologic conditions. In culture, endothelial cells secrete vWf multimers with a broad range of molecular weights, with smaller forms predominating. Larger molecular weight protein multimers are stored in intracellular Wiebel-Palade bodies [14-16] which degranulate in response to inflammatory agents such as phorbol-12-myristate-13-acetate [17], histamine [18], fibrin [19], and thrombin [20]. While high molecular weight vWf is a normal constituent of the subendothelial matrix, the smaller multimers are found in plasma [21]. In vitro, large multimers avidly bind platelets and extracellular matrix [22], thereby mediating platelet aggregation and adhesion to areas of endothelial denudation [23,24]. In disease states, high molecular weight vWf may serve to enhance pathologic platelet-endothelium or platelet-subendothelium interactions which, in concert with other prothrombotic changes, may result in microvascular thrombosis. Increased plasma vWf has been used to monitor vascular involvement in various disease states including rheumatologic diseases [25], primary pulmonary hypertension [26], nephritis [27], myocardial infarction [28], diabetic angiopathy [29], severe infection [30], and acute respiratory distress syndrome (ARDS) [31,32]. Several studies have been performed to elucidate the mechanisms underlying enhanced vWf release in infection, predominantly focusing on the roles of endotoxin and cytokines. In vitro experiments evaluating the direct effects of vWf release from endothelial cells in culture have yielded conflicting results [18,33-38]. In healthy humans, however, endotoxin caused a significant increase in vWf levels 2 to 3 hrs after infusion [39-41] while TNF infusion resulted in a significant increase in vWf levels after 45 mins [42]. The differential time course of increased vWf levels after TNF and endotoxin infusions suggests that TNF is an intermediate factor in endotoxin-induced vWf release [41]. Since increased serum vWf is a postulated marker of endothelial cell injury, investigators have sought to establish its predictive value in patients at risk for developing ARDS [39-42]. These investigations were based on the premise that inereased levels of vWf originated specifically from damage to the pulmonary vasculature. The results have been inconclusive. In the present study, we hypothesize that increased serum vWf levels in critically ill patients are related to generalized endothelial cell activation and subsequent...