Dr. Bokoch’s Research

Endothelial Activation by Liver Reperfusion Injury in Transplantation

Ischemia-reperfusion (I-R) injury during liver transplantation (LT) is a profound inflammatory phenomenon that injures remote organs and worsens patient outcomes. The rising global need for LT has increased use of marginal quality grafts such as those with steatosis or from donors after cardiac death. Coagulopathy and acute kidney injury often arise after reperfusion of marginal grafts. These observations suggest a mechanism of pathologic endothelial activation downstream of liver I-R. I hypothesize that liver I-R releases endogenous Toll-like receptor (TLR) agonists into the circulation that trigger diffuse endothelial activation and dysfunction. In this translational proposal, human serum collected from LT patients at baseline and following reperfusion of the liver graft will be applied to cultured endothelial cells (ECs). Aim 1 will characterize the in vivo state of inflammation and endothelial activation during LT before and after liver I-R. We’ll measure circulating blood markers and perform histology on native blood vessels collected from liver transplant recipients. Aim 2 tests the ability of sera from LT patients to activate ECs ex vivo. Assays of endothelial permeability will be performed, cytokine production, neutrophil adhesion, and expression of coagulation pathway intermediaries to characterize the phenotype of EC activation. To probe the mechanisms by which liver I-R triggers endothelial dysfunction, innate immune signaling pathways will be disrupted using inhibitors, antibodies, and siRNA knockdown. Specifically, the hypothesis will test that LT serum activates ECs through TLR4 signaling stimulated by high-mobility group box 1, a damage-associated molecular pattern. Successful completion of this work will elucidate mechanisms by which inflammation and I-R injury drive endothelial activation, which is of broad relevance to the fields of anesthesia and critical care in addition to liver transplantation.

Related Publications

Serum from patients with cirrhosis undergoing liver transplantation induces permeability in human pulmonary microvascular endothelial cells ex vivo
Michael P. Bokoch et al.

Patients with cirrhosis undergoing liver transplantation frequently exhibit systemic inflammation, coagulation derangements, and edema suggestive of endothelial dysfunction. This syndrome may worsen after ischemia-reperfusion of the liver graft, coincident with organ dysfunction that worsens patient outcomes. Researchers hypothesized that sera from these patients would increase permeability in cultured human endothelial cells ex vivo.  Blood was collected at five time points, spanning the entire liver transplant operation, from adults with cirrhosis presenting for liver transplantation. Findings show that liver transplant sera induced more endothelial cell permeability than serum from healthy human subjects.

The results confirmed the hypothesis that serum from patients undergoing liver transplantation does in fact induce permeability in endothelial cells ex vivo. This finding demonstrates that circulating factors present during liver transplantation can reduce endothelial barrier function and increase endothelial permeability and may contribute to organ injury and present a potential target for future therapeutics.

Angiotensin II in liver transplantation (AngLT-1): protocol of a randomised, double-blind, placebo-controlled trial
Michael P. Bokoch et al.

50 subjects were recruited for this double-blind, randomised clinical trial which set out to assess the efficacy of angiotensin II as a second-line vasopressor infusion during liver transplantation. The primary outcome is to measure the dose of norepinephrine required to maintain a mean arterial pressure ≥65 mm Hg. Secondary outcomes include vasopressin or epinephrine requirement and duration of hypotension. Safety outcomes include incidence of thromboembolism within 48 hours of the end of surgery and severe hypertension.  Upon completion of this trial, researchers intend to design of a follow-up, multicentre trial powered to detect a reduction of organ injury in liver transplantation. 

The Association between Vena Cava Implantation Technique and Acute Kidney Injury After Liver Transplantation.
MP Bokoch, et al.

Does the choice of vena cava reconstruction technique during liver transplantation impact Acute Kidney Injury (AKI)? To answer, the authors use a single-center retrospective cohort of 897 liver transplants performed using either the vena cava preserving piggyback technique or caval replacement technique without veno-venous bypass or shunts. They find that Piggyback technique, compared with caval replacement, was associated with a reduced incidence of AKI after liver transplantation. There was no difference in long-term renal outcomes between the 2 groups.

The Yin and Yang of the Renin–Angiotensin–Aldosterone System in Acute Kidney Injury.
M Legrand, MP Bokoch

In this editorial, the authors acknowledge the important cardiac surgery insights gained from the recent study published by Kullmar and colleagues. However, perhaps the hypothesis needs to be balanced and refined as it is necessary to better understand the full profile and timing of RAAS alterations in critical illness and the impact of modulating it, both in the acute and post-acute phase. Additionally, better phenotyping of patients and more well-designed interventional trials are definitely needed.