Cytokine activation of vascular endothelium. Effects on tissue-type plasminogen activator and type 1 plasminogen activator inhibitor

Biology and pathogenesis of thrombosis and procoagulant activity in invasive infections caused by group A streptococci and Clostridium perfringens

Group A streptococcal necrotizing fasciitis/myonecrosis and Clostridium perfringens gas gangrene are two of the most fulminant gram-positive infections in humans. Tissue destruction associated with these infections progresses rapidly to involve an entire extremity. Multiple-organ failure is common, and morbidity and mortality remain high. Systemic activation of coagulation and dysregulation of the anticoagulation pathways contribute to the pathogenesis of many diverse disease entities of infectious etiology, and it has been our hypothesis that microvascular thrombosis contributes to reduced tissue perfusion, hypoxia, and subsequent regional tissue necrosis and organ failure in these invasive gram-positive infections. This article reviews the coagulation, anticoagulation, and fibrinolytic systems from cellular players to cytokines to novel antithrombotic therapies and discusses the mechanisms contributing to occlusive microvascular thrombosis and tissue destruction in invasive group A streptococcal and C. perfringens infections. A thorough understanding of these mechanisms may suggest novel therapeutic targets for patients with these devastating infections.

The role of the endothelium in severe sepsis and multiple organ dysfunction syndrome

Severe sepsis, defined as sepsis with acute organ dysfunction, is associated with high morbidity and mortality rates. The development of novel therapies for sepsis is critically dependent on an understanding of the basic mechanisms of the disease. The pathophysiology of severe sepsis involves a highly complex, integrated response that includes the activation of a number of cell types, inflammatory mediators, and the hemostatic system. Central to this process is an alteration of endothelial cell function. The goals of this article are to (1) provide an overview of sepsis and its complications, (2) discuss the role of the endothelium in orchestrating the host response in sepsis, and (3) emphasize the potential value of the endothelium as a target for sepsis therapy.

Plasminogen activator inhibitor activity is associated with raised lactate levels after cardiac surgery with cardiopulmonary bypass

OBJECTIVE

To investigate the pathophysiology underlying raised lactate levels after cardiac surgery with cardiopulmonary bypass (CPB).

DESIGN

Prospective observational study.

SETTING

Medical and surgical intensive care unit of a tertiary hospital.

PATIENTS

A total of 40 patients undergoing first-time coronary artery bypass grafting with CPB.

INTERVENTIONS

The prothrombotic response to cardiac surgery with CPB was assessed by measuring plasma levels of prothrombin fragment 1 + 2 and plasminogen activator inhibitor (PAI) activity. The hemodynamic responses to cardiac surgery with CPB were also measured using standard techniques.

MEASUREMENTS AND MAIN RESULTS

After cardiac surgery, prothrombin fragment 1 + 2 levels increased 6-fold and PAI activity increase 2- to 3-fold (p <.0001). Lactate levels were not associated with prothrombin fragment 1 + 2 and PAI activity levels after CPB. Lactate levels were associated with baseline PAI activity (p =.006), a history of hypertension (p =.02), raised baseline lactate levels (p =.02), an early increase in body temperature after CPB (p =.05), a late increase in oxygen consumption after CPB (p =.03), and a raised white cell count after CPB (p =.06). Lactate levels were inversely associated with the maximum activated clotting time level reached during CPB (p =.02). Multivariate linear regression demonstrated lactate levels were independently associated with baseline PAI activity.

CONCLUSION

We found cardiac surgery with CPB was associated with a marked prothrombotic response. Lactate levels were associated with elevated baseline PAI activity and evidence of an amplified inflammatory response to cardiac surgery with CPB. Our findings implicate aspects of the inflammatory response, including microvascular thrombosis, in the development of raised lactate levels after cardiac surgery with CPB.

C-reactive protein increases plasminogen activator inhibitor-1 expression and activity in human aortic endothelial cells: implications for the metabolic syndrome and atherothrombosis

BACKGROUND

Inflammation plays a pivotal role in atherosclerosis. In addition to being a risk marker for cardiovascular disease, much recent data suggest that C-reactive protein (CRP) promotes atherogenesis via effects on monocytes and endothelial cells. The metabolic syndrome is associated with significantly elevated levels of CRP. Plasminogen activator inhibitor-1 (PAI-1), a marker of atherothrombosis, is also elevated in the metabolic syndrome and in diabetes, and endothelial cells are the major source of PAI-1. However, there are no studies examining the effect of CRP on PAI-1 in human aortic endothelial cells (HAECs).

METHODS AND RESULTS

Incubation of HAECs with CRP results in a time- and dose-dependent increase in secreted PAI-1 antigen, PAI-1 activity, intracellular PAI-1 protein, and PAI-1 mRNA. CRP stabilizes PAI-1 mRNA. Inhibitors of endothelial NO synthase, blocking antibodies to interleukin-6 and an endothelin-1 receptor blocker, fail to attenuate the effect of CRP on PAI-1. CRP additionally increased PAI-1 under hyperglycemic conditions.

CONCLUSIONS

This study makes the novel observation that CRP induces PAI-1 expression and activity in HAECs and thus has implications for both the metabolic syndrome and atherothrombosis.

Suppression of the release of type-1 plasminogen activator inhibitor from human vascular endothelial cells by Hawaii deep sea water

The effect of deep sea water on the fibrinolytic properties of human vascular endothelial cells was investigated. There was no difference in the growth ratio between human umbilical vein endothelial cells (HUVECs) cultured with growth medium (RPMI-1640 containing 20% fetal calf serum) prepared with Hawaii deep sea water (HDSW medium) and those with medium prepared with normal distilled water (control medium). The secretion of type 1 plasminogen activator inhibitor (PAI-1) from HUVECs was significantly reduced by about twofold. However, the levels of PAI-1 mRNA in HUVECs cultured with HDSW medium did not change when compared with those cultured with control medium. Though HDSW medium also reduced the secretion of tissue-type plasminogen activator, the suppressive effect was more prominent for PAI-1. Thus, the balance of fibrinolytic activity was turned toward anti-thrombotic in HUVECs. This was evidenced by the lysis of 125I-fibrin clot in the presence of plasminogen. That is, HUVECs cultured with HDSW medium degraded 125I-fibrin more efficiently than HUVECs with control medium. Such enhanced clot lysis was maintained as long as HDSW medium was present. The accelerated effect of HDSW medium on clot lysis disappeared after the exchange of HDSW medium to control medium. These findings suggest that HDSW may specifically and predominantly affect the process of molecular transfer of PAI-1 after its transcription, resulting in an enhanced fibrinolytic activity of HUVECs. Since HDSW reduces the thrombotic potential of cultured HUVECs, it is speculated that the materials contained in HDSW may prevent the incidence of thrombotic disorders.

Modulation of the expression of tissue plasminogen activator and its inhibitor by hypoxia in human peritoneal and adhesion fibroblasts

OBJECTIVE

To determine whether normal peritoneal and adhesion fibroblasts express tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI-I) and whether their expression is regulated by oxygen.

DESIGN

Prospective experimental study.

SETTING

University medical center.

PATIENT(S)

Cultures of human fibroblasts established from peritoneal and adhesion tissues. Hypoxia treatment of the primary cultured fibroblasts.

MAIN OUTCOME MEASURE(S)

We have used the multiplex reverse transcription polymerase chain reaction (RT-PCR) technique to determine the effect of hypoxia on the expression of tPA and PAI-I in normal peritoneal (NPF) and adhesion (ADF) fibroblasts. Cultures of NPF and ADF were exposed to hypoxia (2% O(2)) for 24 hours. RNA was extracted from cells and subjected to multiplex RT-PCR to quantitate relative changes in mRNA levels of tPA and PAI-I in response to hypoxia treatment.

RESULT(S)

Basal tPA mRNA levels are present in both NPF and ADF and were 45% higher in NPF than ADF. Hypoxia decreased tPA in both NPF and ADF by 74% and 95%, respectively. Basal PAI-I mRNA levels were 64% higher in ADF than in NPF. Hypoxia increased PAI-I mRNA levels by 67% and 53% in NPF and ADF, respectively.

CONCLUSION(S)

Plasminogen activator activity (PAA) of the peritoneum does not solely reside in the mesothelial cells, as previously identified, but also exists within fibroblasts, thus providing the potential to resolve postoperative fibrinous collections even at sites at which the mesothelial cells have been injured, removed, or destroyed. Furthermore, PAA in fibroblasts is regulated by oxygen; creation of a hypoxic state markedly attenuates PAA, thereby leading to adhesion development.

Increased Expression of Plasminogen Activator Inhibitor-1 by Mediators of the Acute Phase Response: a Potential Progenitor of Vasculopathy in Hypertensives

Hypertension is an important risk factor for coronary atherosclerosis, which is accelerated by inflammation and diminished fibrinolysis. We have previously shown that levels of plasminogen activator inhibitor-1 (PAI-1), the major physiologic inhibitor of fibrinolysis, are increased with atherogenic metabolic derangement. Because the liver is one of the major sources of circulating PAI-1, we here examined the effects of two proinflammatory cytokines, interleukin (IL)-1beta, and IL-6, on PAI-1 production in a human hepatoma cell line, HepG2. IL-1beta (1 ng/ml) and IL-6 (1 ng/ml) increased the accumulation of PAI-1 in the conditioned media over 24 h (IL-1beta: 2.1 +/- 0.2 (mean +/- SD) fold over the control; IL-6:1.4 +/- 0.2 fold; Western blot, p < 0.05). The increase in PAI-1 protein accumulation correlated with the increased expression of PAI-1 mRNA (Northern blot). An HMG-CoA reductase inhibitor (mevastatin, 10 micromol/l) attenuated the PAI-1 production induced by IL-1beta and IL-6. The plasma PAI-1 activity level was higher in hypertensives than in normotensives (10.0 +/- 9.8 AU/ml vs. 6.2 +/- 4.5 AU/ml, p < 0.05). The plasma PAI-1 antigen level was also higher in hypertensives than in normotensives (30.9 +/- 22.4 ng/ml vs. 24.4 +/- 13.3 ng/ml, p < 0.05). Thus, 1) IL-1beta and IL-6 can increase PAI-1 production in hepatic cells and 2) mevastatin may exert anti-thrombotic effects by decreasing the PAI-1 protein production induced by these proinflammatory cytokines. These results provide further insights into how inflammation is involved in the atherothrombotic complications observed in hypertensives, which may be ameliorated by HMG-CoA reductase inhibitors.

Positive Chlamydia pneumoniae serology is associated with elevated levels of tumor necrosis factor alpha in patients with coronary heart disease

Infectious agents are possible stimulators of inflammation in atherogenesis. The aim of this study was to investigate if Chlamydia pneumoniae and Helicobacter pylori were associated with elevated levels of tumor necrosis factor alpha (TNFalpha) and interleukin-6 in coronary heart disease (CHD) patients (n=193) and age- and sex-matched controls (n=193) as markers of increased inflammatory activity. C reactive protein (CRP) and fibrinogen were also included. Serologic status towards the two bacteria was measured and levels of the inflammatory markers were compared between seropositives and seronegatives, each study group being evaluated separately. In CHD patients Chlamydia lipopolysaccharide (LPS) IgA seropositivity predicted elevated TNFalpha levels (P=0.009), still statistically significant after adjustment for traditional cardiovascular risk factors (P=0.005). Chlamydia LPS IgG seropositivity independently predicted fibrinogen levels in CHD patients (P=0.028), while no association between serology and inflammatory markers were observed among controls. H. pylori seropositivity alone was not associated with any increase in the inflammatory markers in any of the two groups. However, in CHD patients seropositivity to both agents predicted higher levels of TNFalpha (P=0.041), CRP (P=0.037) and fibrinogen (P=0.001) compared to double seronegativity. We conclude that C. pneumoniae LPS seropositivity may contribute to increased vascular inflammation in CHD patients, possibly even more pronounced when present in combination with H. pylori seropositivity.

Endogenous prostaglandin D2 synthesis reduces an increase in plasminogen activator inhibitor-1 following interleukin stimulation in bovine endothelial cells

OBJECTIVE

We examined the role of prostaglandin D2 (PGD2) in the formation of plasminogen activator inhibitor (PAI)-1 following interleukin-1beta (IL-1) stimulation in bovine endothelial cells (EC) transfected with lipocaline-type PGD2 synthase (L-PGDS) genes.

DESIGN AND METHODS

EC were isolated from bovine thoracic aorta and incubated with 20 U/ml IL-1 and various concentrations of authentic PGD2. The isolated EC were also transfected with L-PGDS genes by electroporation. The L-PGDS-transfected EC were used to investigate the role of endogenous PGD2 in IL-1 stimulated PAI-1 biosynthesis. We also used an anti-PGD2 antibody to examine whether an intracrine mechanism was involved in PAI-1 production. PGD2 and PAI-1 levels were determined by radio- and enzyme-immunoassay, respectively. PAI-1 mRNA was assessed by reverse transcription-polymerase chain reaction.

RESULT

IL-1 stimulated PAI-1 production by EC was dose-dependently inhibited by authentic PGD2 at concentrations greater than 10-6 mol/l. L-PGDS gene-transfected EC produced more PGD2 than EC transfected with the reporter gene alone. IL-1 induced increases in PAI-1 production in EC transfected with reporter genes alone. However, this effect was significantly attenuated in the case of IL-1 stimulation of EC transfected with L-PGDS genes, and accompanied by an apparent suppression of PAI-1 mRNA expression. The effects of PGD2 on PAI-I formation were reversed to the basal levels by the inhibition of synthesis of endogenous PGD2. Neutralization of extracellular PGD2 by anti-PGD2 antibody influenced neither PAI-1 mRNA expression nor PAI-1 biosynthesis.

CONCLUSION

EC transfected with L-PGDS genes increased PGD2 synthesis. This was associated with attenuation of both PAI-1 formation and PAI-1 mRNA expression. It is suggested that endogenous PGD2 decreases PAI-1 synthesis and PAI-1 mRNA expression, probably through an intracrine mechanism.

Hypoxia enhances the expression of plasminogen activator inhibitor-1 in human lung cancer cells, EBC-1

Plasminogen activator inhibitor-1 (PAI-1) is one of the target genes of hypoxia inducible factor-1alpha (HIF-1alpha). Besides being an important physiological regulator of the fibrinolytic system PAI-1 is also involved in cancer invasiveness. HIF-1alpha is expressed in various types of pulmonary cells, but the relation of PAI-1 to HIF-1alpha under hypoxic condition in these cells are not fully elucidated. We, therefore, studied the effect of hypoxia on the expression of PAI-1 in a lung cancer cell line EBC-1. The expression of HIF-1alpha protein in EBC-1 cells was enhanced by hypoxia, and this was associated with increased secretion of PAI-1. Hypoxia did not affect the levels of HIF-1alpha mRNA but enhanced the PAI-1 mRNA. Pretreatment of the cells with MG132, which inhibits the proteasomal degradation of HIF-1alpha, increased the production of PAI-1 under both normoxia and hypoxia. We conclude that hypoxia induces PAI-1 expression, in EBC-1 cells, through the stabilization of HIF-1 complex and this may be related to cancer metastasis.

Histopathology of cardiac xenograft rejection in the pig-to-baboon model

BACKGROUND

The use of pig organs transgenic for human decay accelerating factor (hDAF) has largely overcome the problems of hyperacute rejection. With improved immunosuppressive protocols, life supporting grafts are showing greater survival times bringing the possibility of clinical xenotransplantation closer. Examination of the histopathology of the rejection process provides insight into the underlying mechanism and may suggest ways in which new immunosuppressive strategies should be directed.

METHODS

44 baboons (Papio anubis) underwent heart transplants of which 39 were from transgenic donors. The transplanted organs were examined histologically and stained for evidence of immunoglobulin and complement deposition as well as cellular infiltrates.

RESULTS

In the transgenic animals survival times were 2 to 99 days (mean 23.5) and the heterotopic group and 1 to 39 days (mean 11.7) in the orthotopic group. There were 3 cases of hyperacute rejection between the 2 groups. Rejected organs showed areas of old and recent myocardial infarction associated with vascular thrombosis. There was widespread deposition within vessels of immunoglobulins IgM and IgG together with complement fractions C3 and C5b to 9 in those organs that were rejected. The amount of complement positive in the longer surviving organs was less than those rejecting early. Cellular infiltate was predominantly macrophage with some later appearing T or natural killer cells.

CONCLUSIONS

The histopathological changes support the importance of immunoglobulin and complement in delayed xenograft or acute vascular rejection. With time there is an increase in cellular infiltrate predominantly macrophages and these findings suggest an increasingly important role for the cells and the rejection process. The presence of areas of infarction and underlying vascular thrombosis is in keeping with endothelial activation and the establishment of procoagulant phenotype which may be due to immunoglobulin, complement, secreted cytokines and direct cellular effects.

Expression of glomerular plasminogen activator inhibitor type 1 in glomerulonephritis

Plasminogen activator inhibitor type 1 (PAI-1) and tissue plasminogen activator (tPA) are the major regulators of plasmin generation. Glomerular PAI-1/tPA balance is involved in extracellular matrix turnover, as well as fibrin deposition in glomeruli. Renal biopsy specimens were obtained from 80 patients with either primary or secondary glomerulonephritis (10 patients, minimal change nephrotic syndrome; 6 patients, focal segmental glomerulosclerosis [FSGS]; 10 patients, membranous nephropathy [MN]; 24 patients, mesangial proliferative glomerulonephritis; 15 patients, lupus nephritis; 14 patients, diabetic nephropathy; and 1 patient, membranoproliferative glomerulonephritis). We quantified glomerular PAI-1 and tPA messenger RNA (mRNA) by competitive polymerase chain reaction. We also determined PAI-1 mRNA localization by in situ hybridization. Glomerular PAI-1 mRNA levels in patients with FSGS and MN were significantly greater than those of controls. There was a sixfold increase in PAI-1-tPA mRNA ratio in patients with MN compared with the control group. In addition, glomerular PAI-1 mRNA level correlated with level of proteinuria. Conversely, there was no difference in tPA mRNA levels among types of glomerulonephritis. These results suggest that suppressed glomerular fibrinolytic and proteolytic activity may be associated with the pathogenesis of glomerulonephritis, especially in FSGS and MN.

Plasminogen activator inhibitor-1 is a major stress-regulated gene: implications for stress-induced thrombosis in aged individuals

Plasminogen activator inhibitor-1 (PAI-1) is one of the primary inhibitors of the fibrinolytic system and has been implicated in a variety of thrombotic disorders. In this report, stress-induced changes in murine PAI-1 gene expression were investigated to study the role of this inhibitor in the development of stress-induced hypercoagulability. Restraint stress led to a dramatic induction of plasma PAI-1 antigen and of tissue PAI-1 mRNA with maximum induction in adipose tissues. In situ hybridization analysis of the stressed mice revealed that strong signals for PAI-1 mRNA were localized to hepatocytes, renal tubular epithelial cells, adrenomedullar chromaffin cells, neural cells in the paraaortic sympathetic ganglion, vascular smooth muscle cells, and adipocytes, but not to endothelial cells. These observations indicate that the stress induces the PAI-1 gene expression in a tissue-specific and cell type-specific manner. The induction of PAI-1 mRNA by restraint stress was greater than that observed for heat shock protein, a typical stress protein, suggesting that PAI-1 is one of the most highly induced stress proteins. Importantly, the magnitude of induction of PAI-1 mRNA by stress increased markedly with age, and this increase in PAI-1 correlated with tissue thrombosis in the older stressed mice. Moreover, much less tissue thrombosis was induced by restraint stress in young and aged PAI-1-deficient mice compared with age-matched wild-type mice. These results suggest that the large induction of PAI-1 by stress increases the risk for thrombosis in the older populations, and that the adipose tissue may be involved.

Cytokine-induced expression of tPA is differentially modulated by NO and ROS in rat mesangial cells

BACKGROUND

Dysregulated expression of diverse proteases and their specific inhibitors is critical for the increase in extracellular matrix accumulation that accompanies chronic inflammatory and sclerotic processes within the renal mesangium. Within the activating cascade of several proteases, the plasminogen system plays an important role.

METHODS

We tested for modulatory effects of the nitric oxide (NO) donors S-nitroso-N-acetyl-D,L-penicillamine and DETA-NONOate, and the superoxide-generating system hypoxanthine/xanthine oxidase (HXXO) on the expression and activity of tissue plasminogen activator (tPA) by ELISA and Northern blotting.

RESULTS

Interleukin-1beta (IL-1beta)-induced tPA and plasminogen activator inhibitor (PAI)-1 mRNA and supernatant tPA antigen were significantly inhibited by both NO donors, which resulted in a net decrease in the IL-1beta-evoked tPA enzyme activity in the conditioned media. Addition of the NO-synthase inhibitor N-monomethyl l-arginine markedly increased the cytokine-triggered tPA- and PAI-1 mRNA levels, respectively. In contrast, HXXO caused a marked amplification of the IL-1beta-induced steady-state tPA mRNA level and tPA enzyme activity that was blocked by catalase. Since MnTBAP, a superoxide dismutase mimetic, had no effects on the amplification of mRNA levels, we suggest that H2O2 is the candidate reactive oxygen species (ROS) responsible for the potentiation of IL-1beta-triggered tPA and PAI-1 expression.

CONCLUSIONS

The temporal relationship between NO and ROS generation is a critical step in the modulation of tPA and PAI-1 expression in mesangial cells and may account for a dysregulation of matrix turnover during inflammatory processes in the renal mesangium.

IL-1beta down-regulates tissue-type plasminogen activator by up-regulating low-density lipoprotein receptor-related protein in AML 12 cells

Interleukin-1 (IL-1) regulation of tPA in hepatocytes was studied in mouse hepatocyte line AML12. IL-1 induced transient accumulation of tPA mRNA as high as threefold by 2 h after the start of treatment. The cytokine also induced the mRNA for serum amyloid A, a typical acute-phase protein in mice, with more sustained kinetics in a time-dependent manner. In contrast to the induction of mRNA, tPA activity and protein levels in the harvested medium were dramatically diminished by IL-1. IL-1 stimulated the uptake of (125)I-tPA by AML 12. This uptake was inhibited by 39-kDa receptor-associated protein (RAP), but not by the sugar mannan. These results revealed that low-density lipoprotein receptor-related protein (LRP), which is known to be a receptor for tPA and to be blocked by RAP, was up-regulated by IL-1. We also demonstrated, for the first time, that IL-1 transiently increased the mRNA level of LRP threefold by 30 min after the start of IL-1 treatment of AML 12. The receptor-mediated endocytosis of tPA by hepatocytes may thus play a crucial role in the down-regulation of fibrinolysis during the acute-phase response.

Endothelial perturbation in children and adolescents with type 1 diabetes: association with markers of the inflammatory reaction

OBJECTIVE

The progression of diabetic angiopathy is, in most cases, unpredictable. The aim of this study was to investigate early events that could influence the development of diabetic angiopathy.

RESEARCH DESIGN AND METHODS

Circulating levels of von Willebrand factor (vWF) and tissue-plasminogen activator (tPA), defining endothelial perturbation, were measured in 40 young patients with type 1 diabetes. Patients were divided into two groups according to the duration of diabetes (group A, <1 year; group B, >1 year) and compared with a control group of age- and sex-matched healthy individuals. Prothrombin fragment 1 and 2 (F(1+2)), tumor necrosis factor-alpha (TNF-alpha), and C-reactive protein (CRP) levels were also determined as markers of a prothrombotic state and inflammatory response. A total of 16 of the 20 children in group A were re-examined after 12 months.

RESULTS

Compared with either normal subjects or patients in group B, children in group A showed increased levels of vWF, tPA, F(1+2), TNF-alpha, and CRP. Significant direct correlations between TNF-alpha or CRP and either vWF, tPA, or F(1+2) were observed. Endothelial perturbation was shown in 70% of group A and 20% of group B. After 1 year, 16 of the 20 patients in group A showed a significant reduction in vWF, tPA, F(1+2), TNF-alpha, and CRP levels, whereas endothelial perturbation was reversed in 5 of these patients.

CONCLUSIONS

Endothelial perturbation represents an early and, in some cases, reversible event in the chronology of type 1 diabetes in children. A correlation might exist between the initial inflammatory reaction and the appearance of endothelial perturbation.

Outer membrane vesicles from Neisseria meningitidis: effects on tissue factor and plasminogen activator inhibitor-2 production in human monocytes

Lipopolysaccharide-containing outer membrane vesicles (OMV-LPS) which are spontaneously released from Neisseria meningitidis during logarithmic growth were studied for their ability to induce procoagulant (tissue factor), profibrinolytic (urokinase-type plasminogen activator) and antifibrinolytic (plasminogen activator inhibitor-2) factors in purified human monocytes. Cell-associated tissue factor was 5.0-fold (n=5) increased, peaking after 8 h, in the presence of OMV-LPS (1 microg/ml, final concentration). Plasminogen activator inhibitor-2 release from monocytes was maximal after 24 h OMV-LPS (1 microg/ml) stimulation and 13.7-fold (n=5) increased compared to controls; whereas urokinase-type plasminogen activator antigen in culture medium remained uninfluenced by OMV-LPS. In conclusion, these OMV-induced imbalances favor fibrin deposition in the monocyte microenvironment and is probably of great importance in the development of disseminated intravascular coagulation, microthrombosis and organ dysfunction related to fulminant meningococcal septicemia.

Staging of the pathophysiologic responses of the primate microvasculature to Escherichia coli and endotoxin: examination of the elements of the compensated response and their links to the corresponding uncompensated lethal variants

OBJECTIVE

Review of primate studies of Escherichia coli sepsis and endotoxemia with a reexamination of the rationale for diagnosis and treatment of these multistage disorders.

SETTING

Animal research and intensive care units in a university medical school.

SUBJECTS

Cyanocephalus baboons (E. coli) and normal human subjects (endotoxin).

INTERVENTIONS

Baboon studies: anti-tissue factor, protein C, endothelial protein C receptor, and anti-tumor necrosis factor antibodies, and active site inhibited factor recombinant VIIa and factor Xa.

RESULTS AND CONCLUSIONS

This review concerns the primate microvascular endothelial response to inflammatory and hemostatic stress. Studies of the impact of inflammatory and hemostatic stress on this microvasculature have fallen into four categories. First, studies of pure hemostatic stress using factor Xa phospholipid vesicles showed that blockade of protein C as well as protein C plus tissue plasminogen activator produced a severe but transient consumptive and a lethal thrombotic coagulopathy, respectively. These studies showed that the protein C and fibrinolytic systems can work in tandem to regulate even a severe response if the endothelium is not rendered dysfunctional by metabolic or inflammatory factors. Second, studies of compensated (nonlethal) inflammatory stress using E. coli or endotoxin in baboon and human subjects showed that even under minimal stress in which there is no evidence of overt disseminated intravascular coagulation, injury of the endothelium and activation of neutrophils and hemostatic factors are closely associated. This showed that molecular markers of hemostatic activity could be used to detect microvascular endothelial stress (nonovert disseminated intravascular coagulation) in patients who are compensated but at risk. These studies also showed that the compensated response to inflammatory stress could exhibit two stages, each with its unique inflammatory and hemostatic response signature. The first is driven by vasoactive peptides, cytokines, and thrombin, followed 12 to 14 hrs later by a second stage driven by C-reactive protein/complement complexes, tissue factor, and plasminogen activator inhibitor 1 secondary to oxidative stress after reperfusion. Third, studies of uncompensated (lethal) inflammatory stress using E. coli showed that irreversible thrombosis of the microvasculature was not a link in the lethal chain of events even though inhibition of components of the protein C network (protein C and endothelial protein C receptor) converted compensated responses to sublethal E. coli into uncompensated lethal responses. Fourth, these studies also showed that there were variants of the lethal response ranging from capillary leak and shock to recurrent sustained inflammatory disorders. We believe that each of these variants arises from their sublethal counterparts, depending on underlying or modulating host factors operating at the time of challenge. Such underlying conditions range from preexisting microvascular ischemia, reperfusion, and oxidative stress to alteration or reprogramming of monocyte/macrophage responses (tolerance to hyperresponsiveness). Characterization of these underlying conditions in patients who are at risk should aid in identifying and optimizing management of these variants.

The endothelium in sepsis: source of and a target for inflammation

OBJECTIVE

To discuss a possible role of the endothelium in sepsis.

DATA SOURCES

Studies published in biomedical journals and our own experimental results.

STUDY SELECTION

Studies on endothelial mechanisms in the context of sepsis.

DATA EXTRACTION AND SYNTHESIS

Changes in endothelial cells on activation by inflammatory stimuli are reviewed briefly; potential mechanisms that lead to endothelial damage during sepsis are discussed.

CONCLUSIONS

The endothelium is a key organ involved in the pathogenesis of sepsis. Dysfunction of or injury to the endothelium may be involved in the pathogenesis of multiple organ failure and should be discriminated from activation resulting from stimulation with inflammatory stimuli. Identification of the molecular mechanisms that contribute to endothelial dysfunction or damage is likely to provide novel targets for the treatment of sepsis.

Rapid differential endogenous plasminogen activator expression after acute middle cerebral artery occlusion

BACKGROUND AND PURPOSE

During focal cerebral ischemia, the microvascular matrix (ECM), which participates in microvascular integrity, is degraded and lost when neurons are injured. Loss of microvascular basal lamina antigens coincides with rapid expression of select matrix metalloproteinases (MMPs). Plasminogen activators (PAs) may also play a role in ECM degradation by the generation of plasmin or by MMP activation.

METHODS

The endogenous expressions of tissue-type plasminogen activator (tPA), urokinase (uPA), and PA inhibitor-1 (PAI-1) were quantified in 10-microm frozen sections from ischemic and matched nonischemic basal ganglia and in the plasma of 34 male healthy nonhuman primates before and after middle cerebral artery occlusion (MCA:O).

RESULTS

Within the ischemic basal ganglia, tissue uPA activity and antigen increased significantly within 1 hour after MCA:O (2P<0.005). tPA activity transiently decreased 2 hours after MCA:O (2P=0.01) in concert with an increase in PAI-1 antigen (2P=0.001) but otherwise did not change. The transient decrease in free tPA antigen was marked by an increase in the tPA-PAI-1 complex (2P<0.001). No significant relations to neuronal injury or intracerebral hemorrhage were discerned.

CONCLUSIONS

The rapid increase in endogenous PA activity is mainly due to significant increases in uPA, but not tPA, within the ischemic basal ganglia after MCA:O. This increase and an increase in PAI-1 coincided with latent MMP-2 generation and microvascular ECM degeneration but not neuronal injury.

Down-regulation of murine tissue factor pathway inhibitor mRNA by endotoxin and tumor necrosis factor-alpha in vitro and in vivo

Tissue factor pathway inhibitor (TFPI) is the protease inhibitor that regulates the extrinsic coagulation pathway initiated by the factor VIIa/TF complex. In this study, we first investigated tissue distribution of TFPI mRNA in the mouse and found that TFPI mRNA expression level was by far the highest in the lung, followed by the heart, adrenal, and adipose tissue. Since little has been known concerning the regulation of TFPI gene expression in vivo, we further analyzed the changes in the TFPI mRNA level in murine tissues after intraperitoneal injection of lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1 (IL-1). LPS and TNF-alpha dramatically decreased TFPI mRNA expression in four tissues examined (e.g., lung, heart, kidney, and adipose tissue), whereas the suppressive effect of IL-1 on TFPI mRNA was limited. The down-regulation of TFPI mRNA expression by LPS and TNF-alpha was also observed in cultured mouse endothelial cells and in cardiomyocyte cell lines. The decreased TFPI mRNA expression by LPS and TNF-alpha in tissues and in the specific cell types may contribute to an increase in the local procoagulant potential, resulting in the thrombotic tendency under septic and/or inflammatory conditions.

Heterogeneity in the incidence and clinical manifestations of disseminated intravascular coagulation: a study of 204 cases

The incidence and clinical manifestations of disseminated intravascular coagulation (DIC) were examined in patients with a range of underlying disorders. Out of 1,882 patients suspected as having DIC, 204 cases were diagnosed as suffering from DIC and included in this study. The underlying disorders experienced by the patients were solid tumors (33.8%), hematologic malignancies (12.7%), aortic aneurysm (10.8%), infections (6.4%), post-operative complications (4.4%), liver disease (2.9%), obstetric disorders (2.5%), and miscellaneous diseases (26.5%). The incidence of DIC was 10.8% out of all patients suspected of having DIC, and the etiologies were 10.9% in solid tumors, 10.1% in hematological malignancies, 20.4% in aortic aneurysm, 12.7% in infections, 15.5% in post-operative complications, 15.8% in liver disease, 3.7% in obstetric disorders, and 9.8% in miscellaneous diseases. The clinical manifestations of DIC patients were varying dependent on their etiologies. Most DIC patients with aortic aneurysm (95.5%) and post-operative complications (88.9%) did not reveal any clinical manifestations. Although all of the patients with obstetric disorders had bleeding, only 20.0% of the patients had organ failure. In contrast, although only 15.4% of the patients with infections had bleeding, 76.9% of these patients had organ failure. Bleeding was observed in 31.9-50.0% of DIC patients with liver disease, hematologic malignancies, and solid tumors. Organ failure was observed in 21.7-33.3% of DIC patients with liver disease, hematological malignancies, and solid tumors. Analysis by measurement of plasma levels of antiplasmin and plasmin-antiplasmin complex suggested that excessive fibrinolysis might contribute to the development of bleeding in these DIC patients. Differences in plasma levels of thrombin-antithrombin complex and cross-linked fibrin degradation products could not account for the differences in the incidence of organ failure in the patients. These findings suggest that the clinical manifestation of DIC varies and might not only be a reflection of microthrombus formation but also a reflection of the other underlying pathomechanisms.

Expression of transforming growth factor-beta and tumor necrosis factor-alpha in the plasma and tissues of mice with lupus nephritis

Although elevated levels of transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha) have been implicated in renal disease, the tissue distribution and cellular localization of the induced cytokines is not well established. In this study, we investigated the expression of these cytokines during the progression of lupus nephritis in MRL lpr/lpr mice. The concentration of both cytokines increased in the plasma of these animals in an age-dependent manner, and there was an age-dependent induction of TGF-beta and TNF-alpha mRNAs in their kidneys. Although the increase in TGF-beta mRNA was specific for the kidney, the increase in TNF-alpha mRNA was widespread and also could be demonstrated in the liver, lung, and heart. In situ hybridization analysis of renal tissues from the lupus-prone mice localized TGF-beta mRNA to the glomerulus, and more specifically, to resident glomerular cells and inflammatory cells infiltrating periglomerular spaces in the nephritic lesions. The signals for TNF-alpha mRNA were detected only in inflammatory cells and were distributed throughout the nephritic kidney. Plasminogen activator inhibitor-1 (PAI-1) is known to be elevated in the glomeruli of MRL lpr/lpr mice, and intraperitoneal administration of either TGF-beta or TNF-alpha into normal mice markedly induced the expression of this potent inhibitor of fibrinolysis in renal glomerular or tubular cells in vivo. These results suggest that the increased renal expression of both cytokines may contribute to the development of lupus nephritis in this model and raise the possibility that PAI-1 may be involved. The fact that TGF-beta is specifically induced in the kidney whereas TNF-alpha increases in a variety of tissues, supports the hypothesis that the renal specificity of this disorder reflects the abnormal expression of TGF-beta.

Effect of atorvastatin and fluvastatin on the expression of plasminogen activator inhibitor type-1 in cultured human endothelial cells

Inhibitors of HMG-CoA reductase, namely statins, improve endothelial function independently of their cholesterol-lowering effects. Plasminogen activator inhibitor type-1 (PAI-1) plays a critical role in vascular pathophysiology both at the intra- and extravascular levels. We therefore investigated the effects of atorvastatin (ATOR) and fluvastatin (FLU) on PAI-1 and also tissue-type plasminogen activator (t-PA) synthesis in 20% fetal calf serum-cultured human umbilical vein endothelial cells (HUVEC) stimulated or not by recombinant human pro-inflammatory cytokines, i.e. tumor necrosis factor alpha (TNFalpha) and interleukin 1alpha (IL-1alpha). In non-stimulated HUVEC, ATOR and FLU significantly diminished (-50% at 2.0 micromol/l) the constitutive production of PAI-1 (mRNA level and protein secretion). This effect was prevented by addition of mevalonate (100 micromol/l). In HUVEC cultivated in 20% fetal calf serum, the t-PA antigen accumulation was not significantly altered, whereas in low serum concentration (1%) a significant stimulatory effect of ATOR (+30%) and FLU (+76%) was observed. In TNFalpha-stimulated cells, ATOR and FLU had a modest down-modulating effect (-17 and -20%, respectively) on TNFalpha-induced increase in PAI-1 synthesis. No effect of statins was observed in IL-1alpha-stimulated HUVEC, suggesting that statins do not interfere with the up-regulation of PAI-1 synthesis by pro-inflammatory cytokines. However, ATOR and FLU inhibited the TNFalpha-induced decrease in t-PA release. In conclusion, these results show that statins favorably modulate the expression of fibrinolytic factors produced by human endothelial cells.

Normal endothelial cell function

Endothelial cell functions, primarily involving regulated mediator secretion or altered surface protein expression, are vital for normal homeostasis. Endothelial cells secrete the potent vasodilator and anti-platelet agent prostacyclin and nitric oxide, and also the potent vasoconstrictor peptide endothelin-1; they control the selective adhesion and emigration of leukocytes from the bloodstream; and they are the source of circulating von Willebrand factor, tissue plasminogen activator and type 1 plasminogen activator inhibitor. The properties of healthy endothelium ensure that an antithrombotic and anticoagulant balance is maintained in the bloodstream, and provide a tonic vasodilator action that controls blood flow and pressure on a minute-to-minute basis. Disturbances of normal endothelial function are strongly implicated in the pathogenesis of atherosclerosis and autoimmune vasculitic diseases including lupus.

Hypoxia induces transcription of the plasminogen activator inhibitor-1 gene through genistein-sensitive tyrosine kinase pathways in vascular endothelial cells

A decline in oxygen concentration perturbs endothelial function, which promotes local thrombosis. In this study, we determined whether hypoxia in the range of that observed in pathophysiological hypoxic states stimulates plasminogen activator inhibitor-1 (PAI-1) production in bovine aortic endothelial cells. PAI-1 production, measured by ELISA, was increased by 4.7-fold (P<0.05 versus normoxic control, n=4) at 12 hours after hypoxic stimulation. Northern blot analysis showed the progressive time-dependent increase in the steady-state level of PAI-1 mRNA expression by hypoxia, which reached a 7.5-fold increase (P<0.05 versus control, n=4) at 12 hours. Deferoxamine, which has been known to bind heme protein and to reproduce the hypoxic response, induced PAI-1 production at both the mRNA and protein levels. The half-life of PAI-1 mRNA, as determined by a standard decay assay, was not affected by hypoxia, suggesting that induction of PAI-1 mRNA was regulated mainly at the transcriptional level. Transient transfection assays of the human PAI-1 promoter-luciferase construct indicates that a hypoxia-responsive region lies between -414 and -107 relative to the transcription start site, where no putative hypoxia response element is found. The hypoxia-mediated increase in PAI-1 mRNA levels was attenuated by the tyrosine kinase inhibitors genistein (50 micromol/L) and herbimycin A (1 micromol/L), whereas PD98059 (50 micromol/L, MEK1 inhibitor), SB203580 (10 micromol/L, p38 mitogen-activated protein kinase inhibitor), and calphostin C (1 micromol/L, protein kinase C inhibitor) had no effect on the induction of PAI-1 expression by hypoxia and deferoxamine. Genistein but not daidzein blocked the production of hypoxia- and deferoxamine-induced PAI-1 protein. Thus, we conclude that hypoxia stimulates PAI-1 gene transcription and protein production through a signaling pathway involving genistein-sensitive tyrosine kinases in vascular endothelial cells.

Post-transcriptional regulation of endothelial cell plasminogen activator inhibitor-1 expression during R. rickettsii infection

Intracellular infection of endothelial cells with Rickettsia rickettsii results in increased steady-state levels of plasminogen activator inhibitor-1 (PAI-1) mRNA. Control mechanisms governing such increased expression in response to this novel stimulus have not been defined. In this study, we compared the stability of PAI-1 mRNA in infected and uninfected endothelial cells (EC) and explored the requirement for de novo host cell protein synthesis in the infection-induced increase of steady-state levels. The half-life of PAI-1 mRNA, which is constitutively expressed in cultured EC, increased from 18 h in uninfected EC to greater than 30 h in EC infected for 24 h, a time point at which increases in steady-state PAI-1 mRNA levels are noted. There was no change in stability of gamma-actin due to infection. Nuclear run-on studies revealed no apparent increase in transcription rate at 4, 18 and 24 h. R. rickettsii -induced increase in PAI-1 mRNA was blocked by the eukaryotic protein synthesis inhibitor, cycloheximide, which suggests that this response requires de novo host cell protein synthesis. These results provide evidence that post-transcriptional control mechanisms are operative in the regulation of PAI-1 during R. rickettsii infection.

Interaction between interleukin-6 and the natural anticoagulant system in acute stroke

Inflammatory reactions mediated by cytokines are involved in the pathogenesis of acute stroke. Decrease in circulating levels of protein C (PC) and protein S (PS) induced by inflammatory cytokines has been postulated as a potential mechanism for a procoagulant tendency during acute stroke. The procoagulant state associated with impairments in natural anticoagulants may induce microvascular obstruction leading to a tissue perfusion reduction that worsens cerebral ischemia. Interleukin-6 (IL-6) regulate the synthesis of C4b-binding protein (C4BP), an acute-phase protein that also regulates PS plasma levels. We measured IL-6, C4BP, erythrocyte sedimentation rate (ESR), total and free PS and PC in 44 patients with acute ischemic stroke to determine if IL-6 decreases circulating levels of natural anticoagulants through the C4BP pathway and if these acute changes in natural anticoagulants may have clinical implications. Patients with higher levels of IL-6 had more severe neurologic deficits on admission, greater infarct size, higher levels of acute-phase reactants, and lower levels of free PS. IL-6 was significantly correlated with C4BP, ESR, and free PS levels. PC levels were also lower in the group of patients with greater IL-6, but differences were not statistically significant. No correlations were found between C4BP and natural anticoagulants. Severe neurologic deficit, greater infarct volume, atrial fibrillation, increased levels of inflammatory parameters (ESR and IL-6), and reduced levels of free PS were associated with disabling stroke at 3 months, but only neurologic severity and ESR remained as independent predictors of stroke disability on multiple regression analysis. Inflammatory reactions mediated by IL-6 during the acute phase of stroke influence the modulation of free PS. However, variations in free PS levels do not have implications for clinical outcome in stroke patients. The link between proinflammatory cytokines and free PS in the acute phase of stroke is not related to the C4BP pathway.

Expression of tissue factor mRNA in cardiac xenografts: clues to the pathogenesis of acute vascular rejection

BACKGROUND

Acute vascular rejection destroys vascularized xenografts over a period of hours to days and is now considered the major hurdle to the clinical application of xenotransplantation. The hallmark of acute vascular rejection is diffuse intravascular coagulation; however, the pathogenesis of coagulation is a matter of controversy. One line of evidence points to activated endothelial cells and another to activated inflammatory cells as a source of tissue factor and thus as a primary cause of this lesion. The distinction between the two mechanisms inducing coagulation in the xenograft provides an opportunity for specific intervention.

METHODS

To explore these mechanisms, we studied the expression of tissue factor mRNA by in situ reverse transcriptase-polymerase chain reaction in relation to the histopathologic manifestations of acute vascular rejection in guinea pig hearts transplanted into rats treated by cobra venom factor to avoid the hyperacute rejection.

RESULTS

Three hours after transplantation and before the deposition of fibrin, tissue factor mRNA was expressed in the endothelial cells lining small and medium blood vessels and in smooth muscle cells of guinea pig cardiac xenografts. Sixteen hours after transplantation, while rat tissue factor mRNA was expressed only in occasional infiltrating cells, cardiac xenografts showed prominent deposits of fibrin in small vessels. Maximum expression of tissue factor on rat infiltrating cells was observed 48 hr after transplantation.

CONCLUSIONS

These results suggest that in acute vascular rejection, coagulation is initiated on the donor vascular system, while the procoagulant characteristics of infiltrating cells may reflect a response to tissue injury rather than a cause.

Modulation of collagen synthesis by tumor necrosis factor alpha in cultured vascular smooth muscle cells

Collagen synthesis in vascular smooth muscle cells (SMCs) after exposure to tumor necrosis factor alpha (TNF-alpha) was investigated using a culture system. The synthesis of collagenase-digestible proteins (CDP) and noncollagenous proteins (NCP) was evaluated by the [3H]proline incorporation. It was shown that TNF-alpha markedly suppresses the incorporation of [3H]proline into both CDP and NCP in confluent cultures of SMCs but not in sparse cultures of the cells. Such a marked suppression by TNF-alpha was not observed in confluent bovine aortic endothelial cells and human fibroblastic IMR-90 cells. In confluent SMCs, the synthesis of CDP was more strongly inhibited by TNF-alpha than that of NCP. When the CDP synthesis was stimulated by transforming growth factor beta, TNF-alpha suppressed the stimulation in both confluent and sparse SMCs. Human SMCs synthesized types I, III, IV and V collagens; TNF-alpha markedly decreased the relative proportion of types IV and V. It was therefore suggested that TNF-alpha modulates the collagen synthesis by SMCs depending on their cell density and modifies the formation of atherosclerotic lesions.

Mechanical stress enhances expression and production of plasminogen activator in aging human periodontal ligament cells

Plasminogen activator (PA) converts plasminogen to plasmin, and plasmin activates the kinin cascade and latent extracellular matrix metalloproteases. The periodontal ligament serves to anchor the tooth to the alveolus and functions as a cushion between these hard tissues to migrate occlusal force during mastication. We reported previously that repeated mechanical tension force (MTF) as an experimental model of a traumatic occlusion, increased PA activity in human periodontal ligament derived fibroblast (hPLF) cells. In this study, the influence of in vitro cellular aging on MTF-stimulated PA activity in hPLF cells was studied. Aged hPLF cells produced a significantly higher PA activity when compared with those of young hPLF cells in response to MTF in a time- and magnitude-dependent manner. tPA mRNA levels in aged cells were higher than those in young cells, whereas PAI-1 mRNA remained unchanged and uPA mRNA was not detected. Because MTF-stimulated PA activity from hPLF cells was increased by in vitro cellular aging, aging of the periodontal ligament may affect the severity of the inflammation and the degradation of the extracellular matrix of periodontal ligament tissue by producing a large amount of PA in response to excessive force such as a traumatic occlusion.

In vitro and in vivo expression of interleukin-1alpha and tumor necrosis factor-alpha mRNA in pemphigus vulgaris: interleukin-1alpha and tumor necrosis factor-alpha are involved in acantholysis

Keratinocyte-derived cytokines have been implicated in the pathogenesis of a number of skin diseases. In this study we examined the possible role of keratinocyte-derived cytokines in the development of acantholysis in pemphigus vulgaris. Nineteen patients with pemphigus vulgaris, demonstrating the characteristic clinical, pathologic, and immunopathologic findings were studied. In situ immunolabeling demonstrated the presence of two cytokines interleukin-1alpha and tumor necrosis factor-alpha, in lesional and perilesional areas. Results were confirmed by reverse transcriptase-polymerase chain reaction, demonstrating overexpression of both cytokines in vivo. To study the role of these cytokines in the pathogenesis of pemphigus vulgaris both in vitro and in vivo studies were performed. The results of the in vitro study demonstrated that pemphigus vulgaris IgG induced interleukin-1alpha and tumor necrosis factor-alpha mRNA in the skin. The potential pathogenic role of these mediators was demonstrated by a blocking study using antibodies against human interleukin-1alpha and tumor necrosis factor-alpha in keratinocytes cultures. A combination of anti-interleukin-1alpha and anti-tumor necrosis factor-alpha antibodies inhibited in vitro pemphigus vulgaris IgG induced acantholysis. To confirm the role of interleukin-1 and tumor necrosis factor-alpha in pemphigus, we utilized passive transfer studies using interleukin-1 deficient mice (ICE-/-, interleukin-1beta-/-) and tumor necrosis factor-alpha receptor deficient mice (TNFR1R2-/-). Both groups demonstrated a decreased susceptibility to the passive transfer of pemphigus. Our data support the role of cytokines interleukin-1 and tumor necrosis factor-alpha in the pathogenesis of pemphigus vulgaris.

Comparison of tissue factor pathway in human umbilical vein and adult saphenous vein endothelial cells: implications for newborn hemostasis and for laboratory models of endothelial cell function

In this work we have undertaken a comparative study of human umbilical vein endothelial cells (HUVECs) and human saphenous vein endothelial cells (HSVECs) with respect to functional and antigenic tissue factor (TF), tissue factor pathway inhibitor (TFPI), and TF mRNA. Monolayers of each cell type (passage 2, except where specified) were grown to confluence and then activated for 4 h with either 50 U/mL IL-1-alpha or 10 microg/mL tumor necrosis factor-alpha. Activated factor X appearing in supernatant was measured using a chromogenic assay, and both Northern blots and quantitative RT-PCR were performed to assess concentrations of TF mRNA accompanying activation. The role of TFPI was separately determined by ELISA for supernatant TFPI antigen, and by measurements of production of activated factor X in the presence of 0, 5, 15, or 50 microg/mL of an antibody directed against TFPI. To address a non-TF pathway endothelial cell function, antigenic concentrations of tissue plasminogen activator for both cell types was also determined by ELISA. HUVECs were found to produce 2.4- to 3.5-fold more functional TF. No significant HUVEC-HSVEC differences were detected in TF antigen, supernatant TFPI, anti-TFPI affinity for endothelial cell-associated TFPI, TF mRNA or its amplification products, and tissue plasminogen activator. Immunostaining for TF antigen, however, may have failed to detect a modest HUVEC-HSVEC difference. Our finding with respect to functional TF indicates that HUVECs and HSVECs are not equivalent in terms of models for endothelial cell function in small children versus adults.

Local insulin infusion stimulates expression of plasminogen activator inhibitor-1 and tissue-type plasminogen activator in normal subjects

PURPOSE

Plasma levels of plasminogen activator inhibitor-1 are increased in obesity, hypertension, and diabetes. Their correlation with insulin levels supports the hypothesis that hypofibrinolysis may affect the development of atherosclerotic complications in patients with insulin resistance. To investigate the effect of insulin on fibrinolysis, we evaluated levels of plasminogen activator inhibitor-1 (PAI-1) and tissue plasminogen activator (tPA) antigens during insulin infusion in the forearm vascular beds of 8 healthy subjects.

MATERIALS AND METHODS

Insulin was infused in the brachial artery of each subject to raise local venous concentrations to approximately 100 microU/mL. Blood samples were obtained from the brachial artery and vein at baseline, after 30, 60, 90, and 120 minutes of infusion, and 30 minutes after the end of the infusion.

RESULTS

Following intra-arterial infusion of insulin, forearm blood flow (mean +/- SD) increased progressively from 2.7 +/- 0.6 to 4.0 +/- 0.6 mL/dL/min (P <0.01) and did not return to baseline after the end of the infusion. Plasminogen activator inhibitor-1 balance increased (345 +/- 160 versus 8 +/- 152 fmol/dL/min, P <0.02) at 60 minutes, reaching baseline levels after the end of the infusion. After 90 minutes, tPA balance increased (40 +/- 26 versus 7 +/- 29 fmol/dL/min, P <0.01) with a profile similar to forearm blood flow.

CONCLUSIONS

Local hyperinsulinemia induces regional vasodilation and expression of PAI-1 and tPA antigens. An alteration of this physiological process could be involved in the development of hypofibrinolysis and atherosclerosis in states of insulin resistance.

Retroviral vector-mediated transfer and expression of human tissue plasminogen activator cDNA in bovine brain endothelial cells

OBJECTIVES

Gene transfer of thrombolytic enzymes to vascular endothelial cells may influence the kinetics of intravascular thrombosis. This study defines the potential for gene transfer of tissue plasminogen activator (tPA) into bovine brain endothelial cells (BBEC).

METHODS

The retroviral vectors derived from murine leukemia virus (MuLV) were used to transfer human tPA cDNA to BBEC. The tPA activity, tPA antigen and tPA inhibitor 1 (PAI-1) antigen were determined in the supernatant of transduced (BBEC/tPA) cell cultures by an immunoassay.

RESULTS

The tPA antigen and enzymatic activity in cell culture supernatants of BBEC/tPA transduced cells were 75 ng/ml and 14 IU/ml after 4 days, that was 25 and 28-fold higher compared to the respective values in control cells. The PAI-1 antigen was not affected by tPA cDNA transfer. The Western blot assay of cell lysates confirmed that the majority of tPA in BBEC/tPA transduced cells was in the form of free tPA. While the maximal transduction efficiency of BBEC with an amphotropic MuLV vector was about 15%, a MuLV pseudotyped with vesicular stomatitis virus G glycoprotein envelope achieved high > 90% maximal transduction efficiency.

CONCLUSIONS

The fibrinolytic activity of brain endothelial cells can be enhanced by transferring human tPA cDNA. These findings provide an initial step in implementation of future studies that investigate the use of this technology as an adjunctive treatment for cerebrovascular disease.

Endothelial cell function and thrombosis

The endothelium is pivotal in the control of haemostasis and thrombosis because it is the primary source of many of the major haemostatic regulatory molecules. Healthy endothelial cells, unlike extravascular cells, are anticoagulant and antithrombotic. This is due to the regulated secretion of antiplatelet agents, including prostacyclin and nitric oxide. Following vessel injury, platelet adhesion to exposed matrix requires von Willebrand Factor, another endothelial cell product. Local generation of thrombin causes a series of receptor-mediated endothelial cell functional responses, while the surface of the endothelium is additionally the site for inactivation of thrombin by antithrombin, and its conversion to a coagulation inhibitor by interaction with thrombomodulin. Endothelial cells are also the source of circulating tissue-type plasminogen activator and its inhibitor, and Tissue Factor pathway inhibitor. In disease states, many of these endothelial cell properties are perturbed towards a more procoagulant and prothrombotic phenotype.

Effects of native, triglyceride-enriched, and oxidatively modified LDL on plasminogen activator inhibitor-1 expression in human endothelial cells

Whereas VLDL has consistently been shown to induce a concentration-dependent increase in the expression of plasminogen activator inhibitor-1 (PAI-1) in human umbilical vein endothelial cells (HUVECs) and liver cells, variable effects have been reported for native and oxidatively modified LDL. In the present study, activation of PAI-1 protein and mRNA expression by native LDL (nLDL), UV-oxidized LDL (uvLDL), and triglyceride (TG)-enriched LDL was studied in HUVECs by using different incubation times and a wide range of lipoprotein concentrations. No significant increase of PAI-1 protein expression was observed after 4 hours of incubation with nLDL or uvLDL. However, PAI-1 protein secretion from HUVECs was markedly enhanced after 18 hours of incubation with uvLDL (200% increase at 10 microg/mL). Stimulation of PAI-1 protein expression in HUVECs by nLDL was seen, however, after increasing the TG content of the LDL particle. LDL enriched in phospholipid had no effect on PAI-1 secretion. PAI-1 mRNA levels on northern blot increased in parallel with the activation of PAI-1 protein expression by native and modified forms of LDL. Low concentrations of TG-enriched LDL (10 microg/mL) and higher concentrations of nLDL and uvLDL (100 microg/mL) were found to increase the binding of a VLDL-inducible transcription factor to the PAI-1 promoter. These results indicate that the TG content of the LDL particle influences PAI-1 expression in endothelial cells. Low concentrations of uvLDL enhanced PAI-1 protein and mRNA expression in the HUVECs after an 18-hour incubation but did not influence the VLDL-inducible transcription factor. This suggests that low levels of oxidized LDL increase PAI-1 expression by a different mechanism than VLDL and TG-enriched LDL.

Endothelial cell and hemostatic activation in relation to cytokines in patients with sepsis

Sepsis is commonly associated with disturbances of the hemostatic balance. Most of the pathophysiological changes in sepsis are caused by endotoxin acting directly through endothelial injury or indirectly through release of cytokines with procoagulant effects. The relation between cytokines and hemostatic parameters was assessed in 32 patients with sepsis. Prothrombin fragment 1+2 (F1+2), thrombin-antithrombin III complexes (TAT), tissue type plasminogen activator (t-PA) functional and antigen, plasminogen activator inhibitor-1 (PAI-1), plasminalpha2-antiplasmin complexes (PAP), D-Dimer, thrombomodulin (TM) and von Willebrand factor (vWF) were measured in patients and in 30 healthy subjects. The levels of cytokines TNF-alpha and interleukin-6 (IL-6) also were determined. A significant increase of F1+2, TAT, PAI-1, PAP, and D-Dimer was observed in septic patients as compared with controls (p<0.0001), whereas t-PA activity was significantly reduced (p<0.01). The markers of endothelial cell activation TM, vWF, and t-PA antigen also were elevated significantly as compared with the control group (p<0.01). Finally, we found a marked increase of TNF-alpha and IL-6 (p<0.0001). Whereas the increase of cytokine levels could be partially responsible for the hemostatic activation, it did not correlate with markers of endothelial activation in patients with sepsis.

The presence of infection-related antiphospholipid antibodies in infective endocarditis determines a major risk factor for embolic events

OBJECTIVES

The impact of infection-associated antiphospholipid antibodies (APA) on endothelial cell activation, blood coagulation and fibrinolysis was evaluated in patients with infective endocarditis with and without major embolic events.

BACKGROUND

An embolic event is a common and severe complication of infective endocarditis. Despite the fact that APAs are known to be associated with infectious diseases, their pathogenic role in infective endocarditis has not been clearly defined.

METHODS

The relationship among the occurrence of major embolic events, echocardiographic vegetation size, endothelial cell activation, thrombin generation, fibrinolysis and APA was examined in 91 patients with definite infective endocarditis, including 26 patients with embolic events and 65 control subjects without embolic events.

RESULTS

Overall, 14.3% of patients exhibited elevated APA levels. Embolic events occurred more frequently in patients with elevated levels of APA than in patients without (61.5% vs. 23.1%; p = 0.008). Patients with elevated levels of APA showed higher levels of prothrombin-fragment F1 +2 (p = 0.005), plasminogen-activator inhibitor 1 (p = 0.0002), von Willebrand factor (p = 0.002) and lower levels of activated protein C (p = 0.001) than patients with normal levels of APA. Thrombin generation and endothelial cell activation were both positively correlated with levels of APA. The occurrence of elevated APA levels was frequently associated with structural valve abnormalities (p = 0.01) and vegetations >1.3 cm (p = 0.002).

CONCLUSIONS

Infection-associated elevated APA levels in patients with infective endocarditis are related to endothelial cell activation, thrombin generation and impairment of fibrinolysis. This may contribute to the increased risk for major embolic events in these patients.

Astrocyte regulation of endothelial tissue plasminogen activator in a blood-brain barrier model

Expression of tissue plasminogen activator (tPA) substantially determines endothelial-dependent fibrinolysis. We used a blood-brain barrier (BBB) model to analyze regulation of brain capillary endothelial tPA and its inhibitor, plasminogen activator inhibitor-1 (PAI-1). This model consists of coculture of murine astrocytes with bovine brain capillary endothelial cells grown as capillary-like structures (CS); after 1 week, astrocytes become extensively associated with CS, and the BBB-associated enzyme gamma-glutamyl transpeptidase is present. We measured tPA and PAI-1 mRNA and tPA activity in this model. Reverse transcription-polymerase chain reaction (RT-PCR) studies showed similar tPA and PAI-1 mRNA levels after 1 day mono-culture (endothelial cells only) versus astrocyte-endothelial coculture preparations. After 7 days (i.e., when elements of the BBB are present), astrocyte-endothelial cocultures (compared with endothelial mono-cultures) showed a 50.7%+/-27.1% (mean +/- SD) reduction in tPA mRNA (P < 0.03) and a 183.3%+/-86.9% increase in PAI-1 mRNA expression (P < 0.02). Moreover, 7-day cocultures demonstrated reduced tPA activity compared with mono-cultures (14.6+/-2.9 IU/mL versus 30.2+/-7.7 IU/mL, P < 0.01); 1-day cocultures and mono-cultures had similar tPA activity. These findings demonstrate that astrocytes regulate brain capillary endothelial expression of tPA when elements of the BBB phenotype are present in this model. These data suggest an important role for astrocytes in the regulation of brain capillary endothelial fibrinolysis.

Hepatocyte growth factor prevents lipopolysaccharide-induced hepatic sinusoidal endothelial cell injury and intrasinusoidal fibrin deposition in rats

BACKGROUND

Acute endotoxemia is known to cause activation of Kupffer cells as well as serious injury in parenchymal and nonparenchymal cells in the liver. We have recently shown that a continuous recombinant hepatocyte growth factor (rHGF) supply prevents lipopolysaccharide (LPS)-induced liver injury in rats. As an attempt to elucidate the mechanism, here we investigate the cytoprotective effect of rHGF on sinusoidal endothelial cells (SECs) in LPS-induced liver injury in rats.

MATERIALS AND METHODS

In order to supply rHGF continuously to the liver, syngenic rat fibroblasts genetically modified to secret rat rHGF were implanted in the spleen. Fourteen days after cell implantation, we injected LPS intravenously and evaluated SEC damage histologically and blood chemically.

RESULTS

Phosphotungstic acid-hematoxylin staining revealed that rHGF treatment greatly attenuated intrasinusoidal LPS-induced fibrin deposition. The ultrastructural changes in SECs caused by LPS administration in control rats were barely detectable in rHGF-treated rats. Blood chemical analyses showed that rHGF potently suppressed the LPS-induced increase in serum hyaluronic acid and transaminase levels.

CONCLUSIONS

Our results indicate an important role for HGF in SEC protection in vivo and would suggest a novel therapeutic strategy for liver diseases with SEC injury.

Heterogeneous distribution of macrophages, tumour necrosis factor alpha, tissue factor and fibrinolytic regulators in atherosclerotic vessels

OBJECTIVE

To assess the representativity of small vascular samples with regard to the expression of six important factors in atherosclerotic vessels.

MATERIALS

Circumferential frozen sections of iliac and femoral arteries (n = 9) from patients undergoing reconstructive bypass surgery.

METHODS

Immunohistochemistry with antibodies against macrophages (CD68), tumour necrosis factor alpha, tissue factor, tissue plasminogen activator, urokinase plasminogen activator and plasminogen activator inhibitor type 1. The distribution of these antigens was characterised by computer assisted image analysis. Antigen positive area in randomly chosen samples of varying size was compared with antigen positive area in the whole vessel transections.

RESULTS

Marked heterogeneity was found with respect to the expression of these factors in atherosclerotic vessels. The representativity of samples was highly dependent on the size of the samples. PAI-1 was more evenly expressed compared to the other antigens.

CONCLUSIONS

Estimates of the expression of these factors based on small samples from atherosclerotic arteries are unreliable.