Complement activation during major surgery: the effect of extracorporeal circuits and high-dose aprotinin

Complement C3 activation in the ICU: Disease and therapy as Bonnie and Clyde

Patients in the intensive care unit (ICU) often straddle the divide between life and death. Understanding the complex underlying pathomechanisms relevant to such situations may help intensivists select broadly acting treatment options that can improve the outcome for these patients. As one of the most important defense mechanisms of the innate immune system, the complement system plays a crucial role in a diverse spectrum of diseases that can necessitate ICU admission. Among others, myocardial infarction, acute lung injury/acute respiratory distress syndrome (ARDS), organ failure, and sepsis are characterized by an inadequate complement response, which can potentially be addressed via promising intervention options. Often, ICU monitoring and existing treatment options rely on massive intervention strategies to maintain the function of vital organs, and these approaches can further contribute to an unbalanced complement response. Artificial surfaces of extracorporeal organ support devices, transfusion of blood products, and the application of anticoagulants can all trigger or amplify undesired complement activation. It is, therefore, worth pursuing the evaluation of complement inhibition strategies in the setting of ICU treatment. Recently, clinical studies in COVID-19-related ARDS have shown promising effects of central inhibition at the level of C3 and paved the way for prospective investigation of this approach. In this review, we highlight the fundamental and often neglected role of complement in the ICU, with a special focus on targeted complement inhibition. We will also consider complement substitution therapies to temporarily counteract a disease/treatment-related complement consumption.

Impact of the Share 35 Policy on Perioperative Management and Mortality in Liver Transplantation Recipients

Background

The Share 35 policy was introduced in 2013 by the Organ Procurement and Transplantation Network (OPTN) to increase opportunities of sicker patients to access liver transplantation. However, it has the disadvantage of higher MELD score associated with adverse postoperative transplant outcomes. Early data after implementation of the Share 35 policy showed significantly poorer post-transplantation survival in some UNOS regions. We aimed to analyze the impact of Share 35 on demographics of patients, perioperative management, and perioperative mortality.

Material/Methods

A retrospective analysis of data was performed from an institutional liver transplantation cohort from 1 January 2008 to 31 December 2017. Adult patients who underwent liver transplantation before 2013 were defined as the pre-Share 35 group and the other group was defined as the post-Share 35 group. The MELD score of each patient was calculated at the time of transplantation. Perioperative mortality was defined as death within 30 days after the operation.

Results

A total of 1596 patients underwent liver transplantation. Of those, 895 recipients underwent OLT in the pre-Share 35 era and 737 in the post-Share 35 era. The median MELD score was significantly higher in the post-Share 35 group (30 vs 26, P<0.001) and 45.7% of the post-Share 35 group had MELD scores ≥35. In intraoperative management, patients required significantly more blood component transfusion, intraoperative vasopressor, and fluid replacement. Veno-venous bypass (VVB) usage was significantly higher in the post-Share 35 era (47.2% vs 38.1%, P<0.001). In the subgroup of patients with MELD scores ≥35, the median waiting time was significantly shorter (18.5 vs 14.5 days, P=0.045). Overall perioperative mortality was not significantly difference between groups (P=0.435).

Conclusions

After implementation of the Share 35 policy, we performed liver transplantation in significantly higher medical acuity patients, which required more medical resources to obtain a result comparable to that of the pre-Share 35 era.

Auxiliary activation of the complement system and its importance for the pathophysiology of clinical conditions

Activation and regulation of the cascade systems of the blood (the complement system, the coagulation/contact activation/kallikrein system, and the fibrinolytic system) occurs via activation of zymogen molecules to specific active proteolytic enzymes. Despite the fact that the generated proteases are all present together in the blood, under physiological conditions, the activity of the generated proteases is controlled by endogenous protease inhibitors. Consequently, there is remarkable little crosstalk between the different systems in the fluid phase. This concept review article aims at identifying and describing conditions where the strict system-related control is circumvented. These include clinical settings where massive amounts of proteolytic enzymes are released from tissues, e.g., during pancreatitis or post-traumatic tissue damage, resulting in consumption of the natural substrates of the specific proteases and the available protease inhibitor. Another example of cascade system dysregulation is disseminated intravascular coagulation, with canonical activation of all cascade systems of the blood, also leading to specific substrate and protease inhibitor elimination. The present review explains basic concepts in protease biochemistry of importance to understand clinical conditions with extensive protease activation.

MASP-2 activation is involved in ischemia-related necrotic myocardial injury in humans

BACKGROUND/OBJECTIVES

Insufficient blood supply to the heart results in ischemic injury manifested clinically as myocardial infarction (MI). Following ischemia, inflammation is provoked and related to the clinical outcomes. A recent basic science study indicates that complement factor MASP-2 plays an important role in animal models of ischemia/reperfusion injury. We investigated the role of MASP-2 in human acute myocardial ischemia in two clinical settings: (1) Acute MI, and (2) Open heart surgery.

METHODS

A total of 187 human subjects were enrolled in this study, including 50 healthy individuals, 27 patients who were diagnosed of coronary artery disease (CAD) but without acute MI, 29 patients with acute MI referred for coronary angiography, and 81 cardiac surgery patients with surgically-induced global heart ischemia. Circulating MASP-2 levels were measured by ELISA.

RESULTS

MASP-2 levels in the peripheral circulation were significantly reduced in MI patients compared with those of healthy individuals or of CAD patients without acute MI. The hypothesis that MASP-2 was activated during acute myocardial ischemia was evaluated in cardiac patients undergoing surgically-induced global heart ischemia. MASP-2 was found to be significantly reduced in the coronary circulation of such patients, and the reduction of MASP-2 levels correlated independently with the increase of the myocardial necrosis marker, cardiac troponin I.

CONCLUSIONS

These results indicate an involvement of MASP-2 in ischemia-related necrotic myocardial injury in humans.

Successful C1 inhibitor short-term prophylaxis during redo mitral valve replacement in a patient with hereditary angioedema

Hereditary angioedema is characterized by sudden episodes of nonpitting edema that cause discomfort and pain. Typically the extremities, genitalia, trunk, gastrointestinal tract, face, and larynx are affected by attacks of swelling. Laryngeal swelling carries significant risk for asphyxiation. The disease results from mutations in the C1 esterase inhibitor gene that cause C1 esterase inhibitor deficiency. Attacks of hereditary angioedema result from contact, complement, and fibrinolytic plasma cascade activation, where C1 esterase inhibitor irreversibly binds substrates. Patients with hereditary angioedema cannot replenish C1 esterase inhibitor levels on pace with its binding. When C1 esterase inhibitor is depleted in these patients, vasoactive plasma cascade products cause swelling attacks. Trauma is a known trigger for hereditary angioedema attacks, and patients have been denied surgical procedures because of this risk. However, uncomplicated surgeries have been reported. Appropriate prophylaxis can reduce peri-operative morbidity in these patients, despite proteolytic cascade and complement activation during surgical trauma. We report a case of successful short-term prophylaxis with C1 esterase inhibitor in a 51-year-old man with hereditary angioedema who underwent redo mitral valve reconstructive surgery.

Comparison of surgical methods in liver transplantation: retrohepatic caval resection with venovenous bypass (VVB) versus piggyback (PB) with VVB versus PB without VVB

Use of piggyback technique (PB) and elimination of venovenous bypass (VVB) have been advocated in adult liver transplantation (LT). However, individual contribution of these two modifications on clinical outcomes has not been fully investigated. We performed a retrospective review of 426 LTs within a 3-year period, when three different surgical techniques were employed per the surgeons' preference: retrohepatic caval resection with VVB (RCR+VVB) in 104 patients, PB with VVB (PB+VVB) in 148, and PB without VVB (PB-Only) in 174. The primary outcomes were intraoperative blood transfusion and the patient and graft survivals. Demographic profiles were similar, except younger recipient age in RCR+VVB and fewer number of grafts with cold ischemic time over 16 h in PB-Only. PB-Only required lesser intraoperative red blood cells (P=0.006), fresh frozen plasma (P=0.005), and cell saver return (P=0.007); had less incidence of acute renal failure (P=0.001), better patient survival (P=0.039), and graft survival (P=0.003). The benefits of PB+VVB were only found in shortened total surgical time (P=0.0001) and warm ischemic time (P=0.0001), and less incidence of acute renal failure (P=0.001) than RCR+VVB. PB-Only method seemed to provide the best clinical outcome. The benefit of PB was not fully achieved when it was used with VVB.

Importance of carbohydrate in the interaction of Tamm‐Horsfall protein with complement 1q and inhibition of classical complement activation

Tamm-Horsfall protein (THP) binds strongly to complement 1q (C1q), a key component of the classical complement pathway. The goals of this study were to determine whether THP altered the activation of the classical complement pathway and whether the carbohydrate portion of THP was involved in this glycoprotein's binding to C1q and alteration of complement activation. The ability of THP to prevent complement activation in diluted serum or plasma incubated at 37 degrees C was assessed using both a haemolytic assay with antibody-sensitized sheep RBC and a C4d ELISA. Both these methods showed that THP inhibited activation of the classical complement pathway in a dose-dependent manner. Glycosidases were used to remove most of the carbohydrate from THP. This partially deglycosylated THP bound human IgG with a higher affinity (KD1 = 1.4 nmol/L; KD2 = 0.31 micromol/L) than did intact THP (KD1 = 33.4 nmol/L; KD2 = 31.0 micromol/L). An ELISA showed that removal of carbohydrate from THP reduced, but did not eliminate, the ability of this protein to inhibit binding of C1q to intact THP. Haemolysis assays using antibody-sensitized sheep RBC showed that removal of THP carbohydrate eliminated the ability of THP to protect against complement activation. In conclusion, THP inhibited the activation of the classical complement pathway that occurred in diluted serum or plasma. The carbohydrate moieties of THP appeared to be important in this inhibitory activity.

Aprotinin in coronary operation with cardiopulmonary bypass: does "low-dose" aprotinin inhibit the inflammatory response?

BACKGROUND

Cardiopulmonary bypass induces a systemic inflammatory response. Aprotinin, a nonspecific proteinase inhibitor is known to improve postoperative hemostasis and may modify the inflammatory reaction. This study evaluates the effects of low-dose aprotinin on inflammatory markers in patients scheduled for elective coronary artery bypass grafting.

METHODS

Patients were prospectively randomized into two groups: the control group (C) (n = 14) and the low-dose aprotinin group (A) (n = 15) with (2 x 10(6) KIU = 280 mg) aprotinin added to the pump prime. Cytokine response (interleukin-6, soluble TNF II receptor), terminal complement production (SC5b-9), and neutrophil activation (lactoferrin) were assessed up to 6 hours postoperatively. Clinical data and hemostatic factors including fibrinopeptide A, thrombin-antithrombin complex, D-dimer, and plasmin/alpha2-antiplasmin were investigated.

RESULTS

In both study groups, a significant increase of all inflammatory markers was seen (IL-6, sTNF-IIR, SC5b-9, lactoferrin), p less than 0.001. Peak levels of complement production occurred after protamine administration, whereas cytokine increases were more pronounced postoperatively with marked elevation up to 6 hours. The markers did not differ significantly between groups throughout the study period (p > 0.05 at each time of determination). However, after protamine administration reduced fibrinolysis (D-dimer, plasmin/alpha2-antiplasmin) was detected in group A. Measurements for coagulation (fibrinopeptide A, thrombin-antithrombin complex) were not significantly influenced by aprotinin. The total amount of blood loss during the first 24 hours was significantly reduced in group A (p < 0.02).

CONCLUSIONS

Low-dose aprotinin added to the pump prime does not inhibit the inflammatory response caused by cardiopulmonary bypass, but improves postoperative hemostasis. A potential effect of high-dose aprotinin on inflammatory markers remains to be elucidated.

High-dose aprotinin modulates the balance between proinflammatory and anti-inflammatory responses during coronary artery bypass graft surgery

OBJECTIVE

To rule out the effect of high-dose aprotinin in respect to the balance of proinflammatory and anti-inflammatory mediators induced by cardiopulmonary bypass (CPB).

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

University-affiliated cardiac center.

PARTICIPANTS

Twenty patients scheduled for coronary artery bypass graft surgery.

INTERVENTIONS

In group A patients (n = 10), high-dose aprotinin was administered (2 x 106 KIU pre-CPB, 2 x 10(6) KIU in prime, 500,000 KIU/hr during CPB). In group C patients (n = 10), placebo was used instead. Proinflammatory interleukin (IL)-6, anti-inflammatory IL-1-receptor antagonist, and clinical parameters were measured 8 times perioperatively. The values are presented as mean +/- SEM.

MEASUREMENTS AND MAIN RESULTS

Four hours after CPB, IL-6 concentration reached the maximum value, being significantly lower in group A patients as compared with group C patients (615 +/- 62 pg/mL v 1,409 +/- 253 pg/mL; p = 0.019). On the first postoperative day, the concentration of IL-6 in group A patients remained lower (219 +/- 24 pg/mL v 526 +/- 123 pg/mL; p = 0.015). In contrast, IL-1-receptor antagonist concentration was higher in group A patients as compared with group C patients after CPB (13,857 +/- 4,264 pg/mL v 5,675 +/- 1,832 pg/mL; p = 0.03). Total postoperative blood loss was lower in group A patients as compared with group C patients (648 +/- 64 mL v 1,284 +/- 183 mL; p = 0.002).

CONCLUSIONS

High-dose aprotinin treatment reduced the inflammatory reaction and postoperative blood loss. The anti-inflammatory reaction was significantly enhanced in these patients, which suggests that the physiologic reaction of the organism to reduce the deleterious effects from CPB is more pronounced by using high-dose aprotinin.

Cardiac surgery and the coagulation system

This review focuses on the activation of the haemostatic system during cardiopulmonary bypass. The interaction of different cascade systems are examined, in particular the relation of inflammation with haemostasis. Novel strategies to supplement or replace heparin for anticoagulation during cardiopulmonary bypass have recently been described. Drug approaches to reduce activation of haemostasis reported during the review period are already well established. Their influence on the inflammatory response may offer interesting perspectives for the future.