Recombinant human protein C, protein S and thrombomodulin as antithrombotics

Human recombinant activated protein C-coated stent for the prevention of restenosis in porcine coronary arteries

Activated protein C (APC), an endogenous protein, inhibits inflammation and thrombosis and interrupts the coagulation cascade. Here, we investigated the effect of human recombinant APC on the development of neointimal hyperplasia in porcine coronary arteries. Yukon Choice bare metal stents were coated with 2.6 µg APC/mm(2). Under general anesthesia, APC-coated and bare stents were implanted in the left anterior descending and circumflex coronary arteries of 10 domestic pigs. During the 4-week follow-up, animals were treated with dual antiplatelet therapy and neointimal hyperplasia was evaluated via histology. Scanning electron microscopy indicated successful but unequal coating of stents with APC; nearly complete drug release occurred within 4 h. Enzyme-linked immunosorbent assay revealed that intracoronary stent implantation rapidly increased the levels of monocyte chemoattractant protein-1, an effect that was inhibited by APC release from the coated stent. Fibrin deposition and adventitial inflammation were significantly decreased 1 month after implanting APC-coated stents versus bare stents, paralleled by significantly smaller neointimal area (0.98 ± 0.92 vs. 1.44 ± 0.91 mm(2), P = 0.028), higher lumen area (3.47 ± 0.94 vs. 3.06 ± 0.91 mm(2), P = 0.046), and lower stenosis area (22.2 ± 21.2% vs. 32.1 ± 20.1%, P = 0.034). Endothelialization was complete with APC-coated but not bare (90%) stents. P-selectin immunostaining revealed significantly fewer activated endothelial cells in the neointima in the APC group (4.6 ± 1.9 vs. 11.6 ± 4.1%, P < 0.001). Thus, short exposure of coronary arteries to APC reduced inflammatory responses, neointimal proliferation, and in-stent restenosis, offering a promising therapy to improve clinical outcomes of coronary stenting. However, coating stents with APC for prolonged, controlled drug release remains technically challenging.

Decreased activated protein C levels as a clinical predictor in patients with ST-elevation myocardial infarction

BACKGROUND

Circulating markers that indicate atherosclerotic plaque instability may have diagnostic and prognostic value in patients with acute coronary syndromes. We evaluated activated protein C (APC), which has antithrombotic, anti-inflammatory, and profibrinolytic properties, as a possible clinical predictor in ST-elevation myocardial infarction (STEMI), including return of spontaneous circulation after sudden cardiac arrest.

METHODS

Patients with STEMI whose APC level was measured upon arrival at the emergency room were enrolled in this study (n=335). The primary end point was inhospital death from any cause.

RESULTS

The APC level ranged from 29% to 142% with a median of 80%. The unadjusted death rate increased in a stepwise fashion with decreasing APC levels (33.7% in quartile 1, 12.7% in 2, 6.0% in 3, and 3.6% in 4, P<.001). This association remained significant in subgroups of patients with STEMI only (P=.04) or with return of spontaneous circulation (P=.01). After adjusting for independent predictors of inhospital death, the odds ratio for death among those in the first quartile of APC levels was 9.4 (95% CI 1.1-81.6, P=.04). A cutoff APC level of 65% had the highest combined sensitivity and specificity in predicting death.

CONCLUSIONS

Measuring APC levels provides predictive information for use in risk stratification across the STEMI spectrum. Decreased APC levels may be a unifying feature among patients at high risk for death after STEMI.

Decreased protein C, protein S, and antithrombin levels are predictive of poor outcome in Gram-negative sepsis caused by Burkholderia pseudomallei

BACKGROUND

Acute septicemic melioidosis is associated with systemic release of endotoxin and the proinflammatory cytokines tumor necrosis factor (TNF)-alpha, interleukin-1, and interleukin-6. Excessive release of these cytokines may lead to endothelial injury, depletion of naturally occurring endothelial modulators, microvascular thrombosis, organ failure, and death.

METHOD

Plasma samples drawn at baseline and after initial antimicrobial therapy in 30 patients with suspected acute severe melioidosis were assayed for D-dimer levels, protein C and protein S antigen levels, and antithrombin functional activities.

RESULTS

Both baseline and continued deficiencies of protein C, protein S, and antithrombin were statistically associated with a poor outcome by logistic regression. Baseline D-dimer levels were significantly higher in fatal cases than survivors and correlated inversely with protein C and antithrombin, suggesting both increased fibrin deposition and fibrinolysis.

CONCLUSION

The inflammatory response to systemic Burkholderia pseudomallei infection leads to depletion of the natural endothelial modulators protein C, protein S, and antithrombin. Both baseline and continued deficiency of these endothelial modulators is predictive of poor outcome in melioidosis.

Activated protein C inhibits the release of macrophage inflammatory protein-1-alpha from THP-1 cells and from human monocytes

Several lines of evidence have implicated activated protein C (APC) to be an endogenous inhibitor of the inflammatory septic cascade. APC may exhibit direct anti-inflammatory properties, independent of its antithrombotic effects. Chemokines influence the interaction of monocytes at the endothelium during infection and sepsis and are involved in the molecular events leading to an adverse and lethal outcome of sepsis. Defining regulatory mechanisms on the monocytic release profile of the proinflammatory C-C chemokines macrophage inflammatory protein-1-alpha (MIP-1-alpha) and monocyte chemoattractant protein-1 (MCP-1) might have therapeutic implications for the treatment of sepsis. We established a monocytic cell model of inflammation by the addition of lipopolysaccharide (LPS) and examined the effect of human APC on LPS-stimulated chemokine release from the monocytic cell line THP-1. We found that human APC in supra-physiological concentrations of 2.5-10 microg/ml inhibited the LPS-induced release of the chemokines MIP-1-alpha and MCP-1, as measured by enzyme-linked immunosorbent assays (ELISA) at 6 up to 24 h. In addition to experiments on THP-1 cells, recombinant human APC in concentrations of 50 ng/ml was found to have an inhibiting effect on the release of MIP-1-alpha from freshly isolated mononuclear cells of septic patients. The ability of APC to decrease the release of the C-C chemokine MIP-1-alpha from the monocytic cell line THP-1 and from human monocytes may identify a novel immunomodulatory pathway by which APC exerts its anti-inflammatory action and may contribute to control the inflammatory response in sepsis.

Septic shock, multiple organ failure, and acute respiratory distress syndrome

In 1914, Schottmueller wrote "Septicemia is a state of microbial invasion from a portal of entry into the blood stream which causes signs of illness." In the last few decades, the evidence that sepsis results from an exaggerated systemic inflammatory host response induced by infecting organisms is compelling; inflammatory mediators are the key players in the pathogenesis of septic shock and multiorgan failure. Sepsis and its sequelae represent a continuum of clinical syndrome encompassing systemic inflammation, coagulopathy, and hemodynamic abnormalities. Severe sepsis and septic shock continue to be the major causes of morbidity and mortality in the United States; sepsis deaths currently match mortality from myocardial infarction. Despite significant advances in our understanding of the pathophysiology and technological innovations in the supportive management, mortality from septic shock remains excessive. After many disappointments with strategies to manipulate the inflammatory response, modulation of coagulation cascade to decrease sepsis mortality has become a clinical reality. This review will highlight and discuss recent advances in the pathophysiology and management of sepsis.

Clinical and laboratory effects of recombinant human activated protein C in the treatment of a patient with sepsis-induced multiple organ failure

OBJECTIVES

To evaluate clinical and laboratory effects of the administration of recombinant human activated protein C (rhAPC) in the treatment of a 25-year-old patient with septic shock and multiple organ failure secondary to perinephritic abscesses.

INTERVENTIONS

Intravenous administration of rhAPC-or drotrecogin alfa (activated)-(24 mcg/kg/h) for a total of 80 h as an adjunct to antimicrobial therapy, mechanical ventilation, hemodynamic support, hemodiafiltration and surgical intervention.

MEASUREMENTS AND MAIN RESULTS

The administration of rhAPC was associated with a rapid recovery of the patient's clinical condition reflected by decreasing Sepsis-related Organ Failure Assessment (SOFA) scores. Laboratory parameters monitoring inflammation and coagulopathy improved during the treatment. No drug-related adverse events were noted.

CONCLUSIONS

RhAPC has been observed to have anticoagulant, anti-inflammatory and profibrinolytic properties in vitro and in vivo. This report describes the effects of rhAPC administration on standard laboratory parameters indicating that no single laboratory parameter exists that is capable of monitoring the effects of rhAPC on the coagulation cascade and the clinical course of sepsis. This description of a patient suffering from sepsis-induced multiple organ failure may illustrate a possible beneficial effect of rhAPC on the course of coagulopathy and systemic inflammatory response and provides evidence for rhAPC complementing standard intensive care therapy in severe sepsis.

Modulation of thrombomodulin-dependent activation of human protein C through differential expression of endothelial Smads

Protein C is a plasma protease that in its active form plays a central role in the regulation of vascular function by modulating thrombosis, inflammation, and apoptosis. A central player in this pathway is the cytokine-regulated receptor thrombomodulin (TM), which functions as a co-factor for the thrombin-dependent generation of activated protein C. We have found that tumor necrosis factor-beta (TGF-beta)-dependent suppression of TM on endothelial cells is differentially regulated by endothelial Smad6s and Smad7. Overexpression of Smad6s resulted in activation of a TGF-beta reporter alone and enhanced TGF-beta response. Moreover, Smad6s overexpression suppressed TM and subsequently reduced activated protein C generation. Antisense inhibition of Smad6s expression enhanced the TM-dependent activation of protein C, whereas blocking the inhibitory Smad7 by antisense resulted in reduced TM-dependent activation of protein C. The effect of Smad6s appeared to be due, at least in part, to up-regulation of TGF-beta itself. Immunohistochemistry studies in normal versus atherosclerotic vessels showed that TM levels were suppressed in the endothelium over plaque. Consistent with the in vitro data, we found differential expression of Smad6s and Smad7 in normal versus atherosclerotic vessels, with Smad6s expression low in normal vessels but elevated in atherosclerotic vessels. In contrast, the opposite expression pattern was observed for Smad7. Overall, our results suggest that the relative balance of these intracellular Smads modulate the balance of endothelial function with regard to protein C activation.

Pharmacology, clinical efficacy, and safety of drotrecogin alfa (activated)

The protein C pathway, which plays an important role in maintaining normal hemostasis and is a critical link between the inflammatory and procoagulant host responses to infection, is involved in modulating the coagulation and inflammation associated with severe sepsis. Recombinant human activated protein C (APC), or drotrecogin alfa (activated), shares the intrinsic pharmacologic activity of endogenous APC. In the Recombinant Human Activated Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) trial, drotrecogin alfa (activated) decreased absolute mortality by 6% and relative risk of mortality by 19% compared with placebo. Drotrecogin alfa (activated) is an important advancement in the treatment of adult patients with severe sepsis.

Recombinant human activated protein C attenuates the inflammatory response in endothelium and monocytes by modulating nuclear factor-kappaB

OBJECTIVE

To review the anti-inflammatory and anti-apoptotic properties of drotrecogin alfa (activated) (recombinant human activated protein C), emphasizing its modulatory effects on endothelial nuclear factor-kappaB. We propose a broad anti-inflammatory effect of drotrecogin alfa (activated), acting on both endothelium and monocytes.

DATA SOURCES

A selected review of the published literature on nuclear factor-kappaB, severe sepsis, and the use of drotrecogin alfa (activated) in clinical and preclinical models, together with data derived from preclinical gene profiling of model systems.

DATA EXTRACTION AND SYNTHESIS

Data from the PROWESS trial support the preclinical evidence of an antithrombotic effect of drotrecogin alfa (activated). Anti-inflammatory effects through reduction of thrombin generation and through thrombin-independent mechanisms in mononuclear and endothelial cells are reviewed. Inhibition of apoptosis is used as an example of the protective effect of drotrecogin alfa (activated) on endothelial and mononuclear cell dysfunction.

CONCLUSIONS

Drotrecogin alfa (activated) acts as a modulator of nuclear factor-kappaB to aid in the host immune response in endothelium and monocytes. Extrapolation of gene array findings to explain apoptosis in endothelium and monocytes, coupled with emerging preclinical reports, provides evidence to support the role of drotrecogin alfa (activated) in modulating nuclear factor-kappaB.

Recombinant human activated protein C: a system modulator of vascular function for treatment of severe sepsis

OBJECTIVE

To review the mechanisms of action and rationale for the use of recombinant human activated protein C in the treatment of severe sepsis. Specifically, we focus on the mechanisms of action in the protein C pathway that converge to modulate the pathophysiology of severe inflammatory disease and sepsis. This analysis includes a discussion of the role of activated protein C in directly modulating cell system biology, independent of antithrombotic activity.

DATA SOURCES/STUDY SELECTION

Published research and review articles relating to the protein C pathway, recombinant human protein C, and the role of protein C in sepsis. Data were also derived from broad gene profiling in model systems of endothelial dysfunction.

DATA EXTRACTION AND SYNTHESIS

Relevant studies were included to support discussion of the unique mechanistic aspect of protein C and its role in the pathogenesis of severe sepsis. We discuss the potential of activated protein C as a unique system modulator for the treatment of severe sepsis and other systemic inflammatory responses that result in microvascular coagulopathy, endothelial dysfunction, and vascular bed failure.

CONCLUSIONS

The protein C pathway plays a unique role in modulating vascular function. As an antithrombotic/profibrinolytic agent, it plays a clear role in maintaining vascular patency. Moreover, it has anti-inflammatory properties and appears to play a unique role as an antiapoptotic and endothelial cell survival factor. In states of systemic inflammatory activation, loss of protein C due to consumptive processes results in a compromised ability to modulate coagulation as well as inflammatory and cell survival functions. This compromise leads to vascular dysfunction, end-organ failure, and death. Replacement with recombinant human activated protein C offers a system-modulating approach to improved outcome.

Efficacy and safety of recombinant human activated protein C for severe sepsis

BACKGROUND

Drotrecogin alfa (activated), or recombinant human activated protein C, has antithrombotic, antiinflammatory, and profibrinolytic properties. In a previous study, drotrecogin alfa activated produced dose-dependent reductions in the levels of markers of coagulation and inflammation in patients with severe sepsis. In this phase 3 trial, we assessed whether treatment with drotrecogin alfa activated reduced the rate of death from any cause among patients with severe sepsis.

METHODS

We conducted a randomized, double-blind, placebo-controlled, multicenter trial. Patients with systemic inflammation and organ failure due to acute infection were enrolled and assigned to receive an intravenous infusion of either placebo or drotrecogin alfa activated (24 microg per kilogram of body weight per hour) for a total duration of 96 hours. The prospectively defined primary end point was death from any cause and was assessed 28 days after the start of the infusion. Patients were monitored for adverse events; changes in vital signs, laboratory variables, and the results of microbiologic cultures; and the development of neutralizing antibodies against activated protein C.

RESULTS

A total of 1690 randomized patients were treated (840 in the placebo group and 850 in the drotrecogin alfa activated group). The mortality rate was 30.8 percent in the placebo group and 24.7 percent in the drotrecogin alfa activated group. On the basis of the prospectively defined primary analysis, treatment with drotrecogin alfa activated was associated with a reduction in the relative risk of death of 19.4 percent (95 percent confidence interval, 6.6 to 30.5) and an absolute reduction in the risk of death of 6.1 percent (P=0.005). The incidence of serious bleeding was higher in the drotrecogin alfa activated group than in the placebo group (3.5 percent vs. 2.0 percent, P=0.06).

CONCLUSIONS

Treatment with drotrecogin alfa activated significantly reduces mortality in patients with severe sepsis and may be associated with an increased risk of bleeding.

Anticoagulant Thrombins

Thrombin plays both procoagulant and anticoagulant roles in the blood coagulation cascade. This dual role is influenced allosterically by the binding of Na(+) near the primary specificity pocket of the enzyme. Recent findings demonstrate that it is possible to engineer recombinant thrombins that have practically lost anticoagulant activity but retain their anticoagulant properties. These anticoagulant thrombins bear substitutions in or around the Na(+) binding site, provide important clues on structure-function relations, and offer a promising alternative to current anticoagulant therapies. In addition, they demonstrate the importance of Na(+) as a coagulation factor and broaden our understanding of the function and regulation of all vitamin K-dependent clotting enzymes.