Graft protein C entrapment is associated with reduced phagocyte activation during reperfusion in human liver transplantation

Graft Neutrophil Sequestration and Concomitant Tissue Plasminogen Activator Release During Reperfusion in Clinical Kidney Transplantation

BACKGROUND

Inflammation, coagulation, and fibrinolysis are tightly linked together. Reperfusion after transient ischemia activates both neutrophils, coagulation, and fibrinolysis. Experimental data suggest that tissue plasminogen activator (tPA) regulates renal neutrophil influx in kidney ischemia and reperfusion injury.

METHODS

In 30 patients undergoing kidney transplantation, we measured renal neutrophil sequestration and tPA release from blood samples drawn from the supplying artery and renal vein early after reperfusion. tPA antigen levels were measured using a commercial enzyme-linked immunosorbent assay kit. For each parameter, transrenal difference (Δ) was calculated by subtracting the value of the arterial sample (ingoing blood) from the value of the venous sample (outgoing blood).

RESULTS

Positive transrenal gradients of tPA antigen occurred at 1 minute [Δ = 14 (3-46) ng/mL, P < .01] and 5 minutes [Δ = 5 (-3 to 27) ng/mL, P < .01] after reperfusion. At 5 minutes after reperfusion, a negative transrenal gradient of neutrophils was observed [Δ = -0.17 (-1.45 to 0.24) x 10E9 cells/L, P < .001]. At 1 minute after reperfusion, neutrophil sequestration into the kidney (ie, negative transrenal neutrophil count) correlated significantly with tPA release from the kidney (ie, positive transrenal tPA concentration), (R = -0.513 and P = .006).

CONCLUSIONS

The findings suggest a proinflammatory role for tPA in ischemia and reperfusion injury in human kidney transplantation.

Cell painting with an engineered EPCR to augment the protein C system

The protein C (PC) system conveys beneficial anticoagulant and cytoprotective effects in numerous in vivo disease models. The endothelial protein C receptor (EPCR) plays a central role in these pathways as cofactor for PC activation and by enhancing activated protein C (APC)-mediated protease-activated receptor (PAR) activation. During inflammatory disease, expression of EPCR on cell membranes is often diminished thereby limiting PC activation and APC's effects on cells. Here a caveolae-targeting glycosylphosphatidylinositol (GPI)-anchored EPCR (EPCR-GPI) was engineered to restore EPCR's bioavailability via "cell painting." The painting efficiency of EPCR-GPI on EPCR-depleted endothelial cells was time- and dose-dependent. The EPCR-GPI bioavailability after painting was long lasting since EPCR surface levels reached 400 % of wild-type cells after 2 hours and remained > 200 % for 24 hours. EPCR-GPI painting conveyed APC binding to EPCR-depleted endothelial cells where EPCR was lost due to shedding or shRNA. EPCR painting normalised PC activation on EPCR-depleted cells indicating that EPCR-GPI is functional active on painted cells. Caveolin-1 lipid rafts were enriched in EPCR after painting due to the GPI-anchor targeting caveolae. Accordingly, EPCR painting supported PAR1 and PAR3 cleavage by APC and augmented PAR1-dependent Akt phosphorylation by APC. Thus, EPCR-GPI painting achieved physiological relevant surface levels on endothelial cells, restored APC binding to EPCR-depleted cells, supported PC activation, and enhanced APC-mediated PAR cleavage and cytoprotective signalling. Therefore, EPCR-GPI provides a novel tool to restore the bioavailability and functionality of EPCR on EPCR- depleted and -deficient cells.

Activated protein C plasma levels in the fasting and postprandial states among patients with previous unprovoked venous thromboembolism

INTRODUCTION

The protein C anticoagulant system is of major importance in the regulation of thrombotic risk, but it is not known whether low plasma levels of activated protein C (APC) in vivo reflect a compromised anticoagulant situation with increased thrombotic risk. Previous studies have reported low, normal or increased plasma APC levels in unselected patients with venous thromboembolism (VTE).

MATERIALS AND METHODS

We performed a population-based, case-control study in patients with a previous history of unprovoked VTE and subjected the participants to a standard fat tolerance test (1g fat/kg body weight) in order to promote physiological coagulation activation.

RESULTS

VTE patients had higher BMI (28.3 ± 4.4 kg/m(2) versus 26.3 ± 3.9 kg/m(2), p=0.045) and greater waist circumference (98.2 ± 12.5 cm versus 93.4 ± 13.4 cm, p=0.041) than age and sex matched controls. APC levels were equal in fasting plasma (3.00 ± 0.74 ng/ml and 2.99 ± 0.60 ng/ml, p=0.66) but higher in postprandial plasma (3.18 ± 0.57 ng/ml and 2.81 ± 0.38 ng/ml, p=0.008) collected from VTE patients and controls, respectively. Endogenous thrombin generation in plasma following a standardized meal, assessed by thrombin-antithrombin complex (TAT), increased similarly in both groups, whereas APC increased only among the VTE patients during the postprandial state. Plasma levels of APC increased linearly with TAT in the postprandial state (p for linear trend=0.012).

CONCLUSIONS

Our findings fail to support the hypothesis that low APC levels are linked to increased thrombotic risk in unprovoked VTE, and they suggest that plasma APC is a biomarker of thrombin generation.

Another formula to determine the prognosis of patients with acute liver failure

BACKGROUND/AIMS

King's College Hospital (KCH) criteria and the model for end-stage liver disease (MELD) score are useful and widely-employed prognostic markers for acute liver failure (ALF). We previously reported that liver atrophy is an important prognostic factor for ALF. The aim of the present study was to assess the value of liver volumetry and to generate a new prognostic formula.

METHODS

Computed tomography-derived liver volume (CTLV) and standardized liver volume (SLV) of 30 adult ALF patients were calculated at the time of diagnosis. Patients were assigned to one of two groups: group A consisted of 13 patients who recovered without surgical intervention, and group B consisted of 17 patients who died due to liver failure or who underwent living donor liver transplantation (LDLT).

RESULTS

The median CTLV/SLV ratios of groups A and B were 1.019 and 0.757, respectively (P = 0.0009). The difference was most significant (P = 0.0002) at the probability cutoff point of 0.80 for CTLV/SLV ratio; the sensitivity and specificity were 76.5% and 92.3%, respectively. Serum total bilirubin (TB) levels and CTLV/SLV ratio were selected as independent prognostic factors by multivariate analysis. A prognostic formula including volumetric analysis was established: Z = -2.3813 - [0.15234 x TB (mg/dl)] + [4.5734 x CTLV/SLV] (AUC = 0.87783, P = 0.0002).

CONCLUSIONS

The CTLV/SLV ratio is a very useful marker for predicting the prognosis of adult ALF. Our prognostic formula including only the CTLV/SLV ratio and TB is simple and useful and awaits validation in a future larger-scale prospective study.

Human activated protein C attenuates both hepatic and renal injury caused by hepatic ischemia and reperfusion injury in mice

Hepatic ischemia and reperfusion (IR) injury is a major clinical problem often leading to acute kidney injury characterized by early endothelial cell apoptosis, subsequent neutrophil infiltration, proximal tubule necrosis/inflammation, impaired vascular permeability, and disintegration of the proximal tubule filamentous actin cytoskeleton. Activated protein C is a major physiological anticoagulant with anti-inflammatory and anti-apoptotic activities in endothelial cells. Here we tested if activated protein C would attenuate hepatic and renal injury caused by hepatic ischemia and reperfusion. Both liver and kidney injury were significantly reduced when activated protein C was given immediately before and 2 h after liver reperfusion, in that there was reduced renal endothelial and hepatocyte apoptosis, as well as reduced hepatic and renal tubular necrosis. Further, the administration of activated protein C also reduced the expression of several pro-inflammatory genes, liver and kidney filamentous-actin degradation, and neutrophil infiltration, and resulted in better preservation of vascular permeability of both the liver and kidney than is normally seen after liver ischemia and reperfusion. These protective effects of activated protein C were due to protease-activated receptor-1 modulation since administration of a selective receptor antagonist dose-dependently inhibited its ameliorative effects in both organs after liver ischemia and reperfusion. Our results suggest the powerful multi-organ protective effects of activated protein C may improve outcome in those patients at significant risk of developing acute kidney injury following liver ischemia and reperfusion during transplantation.

High mobility group box 1 protein as a marker of hepatocellular injury in human liver transplantation

High mobility group box 1 protein (HMGB1), a cytokine actively secreted by phagocytes and passively released from necrotic cells, is an inflammatory mediator in experimental hepatic ischemia/reperfusion injury. We characterized its expression in human liver transplantation. In 20 patients, in addition to systemic samples, blood was drawn from portal and hepatic veins during and after reperfusion to assess changes within the graft. Plasma HMGB1, tumor necrosis factor alpha (TNF-alpha), and interleukin-6 (IL-6) levels were measured, and HMGB1 immunohistochemistry was performed on biopsies taken before and after reperfusion. Plasma HMGB1 was undetectable before reperfusion, and levels in systemic circulation peaked after graft reperfusion. At portal declamping, HMGB1 levels were substantially higher in the caval effluent [188 (80-371) ng/mL] than in portal venous blood [0 (0-3) ng/mL, P < 0.001]. HMGB1 release from the graft continued thereafter. HMGB1 levels were not related to TNF-alpha or IL-6 levels. HMGB1 expression was up-regulated in biopsies taken after reperfusion (P = 0.020), with intense hepatocyte and weak neutrophil staining. HMGB1 levels in hepatic venous blood correlated with graft steatosis (r = 0.497, P = 0.03) and peak postoperative alanine aminotransferase levels (r = 0.588, P = 0.008). Our results indicate that HMGB1 originates from the graft and is a marker of hepatocellular injury in human liver transplantation.

Activation of protein C and hemodynamic recovery after coronary artery bypass surgery

OBJECTIVES

Activated protein C is a physiologic anticoagulant that is activated by thrombin and upregulated during coronary artery bypass grafting. We studied the balance between thrombin generation and activated protein C levels during coronary artery bypass grafting and hypothesized that protein C activation during reperfusion is associated with hemodynamic recovery or postoperative myocardial damage.

METHODS

One hundred patients undergoing elective on-pump coronary artery bypass grafting were prospectively studied. Activated protein C, protein C, prothrombin fragment F1+2 (a marker of thrombin generation), and D-dimer (a marker of fibrinolysis) levels were measured preoperatively and at 7 time points during cardiopulmonary bypass and reperfusion and postoperatively. Hemodynamic parameters were measured serially. Cardiac biomarkers (mass of the Mb fraction of creatine kinase and troponin T) were measured postoperatively.

RESULTS

Reperfusion induced a significant increase in thrombin generation. Activated protein C levels peaked after heparin neutralization, when they increased more than 3-fold. Activated protein C levels correlated with F1+2 and D-dimer levels during cardiopulmonary bypass and reperfusion. Even though this correlation peaked during early reperfusion (r = 0.55, P < .001), the ratio of activated protein C to F1+2 decreased during surgical intervention and early reperfusion by 70% from the preoperative level, indicating a marked delay in protein C activation in relation to thrombin generation. Patients in the highest quintile of activated protein C levels during this period had a higher postoperative cardiac index (mean, 3.1 vs 2.5 L x min(-1) x m(-2); P < .05) and lower systemic vascular resistance (mean, 2137 vs 2429 dyne x s x cm(-5) x m(-2); P < .05). Conversely, levels of preoperative activated protein C and activated protein C measured after heparin neutralization were associated with unfavorable hemodynamic recovery postoperatively. Activated protein C or protein C levels were not associated with increased postoperative cardiac biomarkers.

CONCLUSIONS

Reperfusion caused significant thrombin generation that was followed by activation of protein C. The balance of activated protein C with thrombin is associated dynamically with postoperative hemodynamic recovery.