Liver Transplantation and Reticuloendothelial Clearance Capacity
Condition: Hepatic Insufficiency; Liver Insufficiency
MeSH terms: Hepatic Insufficiency; Liver Failure
Study type: Observational

Summary: 
      Study summary: "Liver transplantation and the reticuloendothelial clearance capacity."

      The purpose of this study is to evaluate the effect of liver transplantation on the immune
      system.

      This study will involve the taking of a number of observations but does not involve any
      treatment, which differs from normal care. Indications for transplantation are solely based
      on the best clinical practice, which is usually performed at the department.

      The study measures liver function based on the clearance of different "marker" substances by
      the liver. These substances are given intravenously and their clearance will be measured from
      bloodstream.

      All substances used in this study are registered in the United Kingdom for clinical
      applications and already used in clinical practice over years. They are safe and without any
      risk to harm individuals under study. Furthermore no side effects or any symptoms caused by
      the administration of these substances are expected.

      Measurements of liver function are undertaken before transplantation, 1 and 7 days following
      the transplant. There is no restriction from any of the patient's prescribed medication. All
      blood samples will be removed from the cannula (drip) and will not require repeated
      injections. It is hoped that this research will lead to a greater understanding of the
      effects of liver transplantation on the immune system.
    

Detailed description: 
      Introduction

      Liver cells called hepatocytes undertake the most important metabolic functions of the liver.
      The liver also contains a large number of immune cells called Kupffer cells. These cells act
      as a filter removing bacteria and other dangerous substances from the blood passing through
      the liver. Although we know and understand a great deal about how liver cells behave and
      function after transplant we have no idea what happens to the immune cells in the liver.
      These immune cells make up 85% of the total body reserves of these cells and serve an
      important function by clearing bacteria and bacterial products from the blood. A failure of
      these cells is associated with risk of infection. Infections, blood clotting disorders and
      many other serious medical issues are typical for patients suffering from chronic liver
      failure.

      This study will use microscopic particles of a human protein called albumin in the form of
      microspheres to simulate bacteria in the blood. We can detect these microspheres by attaching
      a radioactive label to the spheres and measuring emission in a detector called a gamma
      counter. The level of radiation is quite small and similar to a bone scan. We have previously
      shown that healthy liver rapidly clears these albumin microspheres from the blood. We have
      also shown previously that after major liver surgery there is a delay in clearance of
      microspheres, which we believe equates to a poorly functioning innate immune system.

      Liver transplantation is the only successful life-extending treatment for patients with
      chronic liver failure and cirrhosis. During liver transplantation it is known that a
      proportion of hepatocytes damaged and recover following the transplant. We want to establish
      the immediate particulate clearance capacity of the liver following transplantation and the
      pattern of recovery one week later. This is used as a surrogate for liver clearance of
      bacteria and bacterial products.

      We also intend to measure the production of a set of proteins called acute phase proteins,
      which are produced by the liver and may be important in helping immune cells recognize
      bacteria. These proteins, also called opsonins, bind to the walls of bacteria and make it
      easier for immune cells to attach to the bacteria and eat them.

      We also want to find out if there is any difference between non-marginal and marginal liver
      grafts and their reticuloendothelial clearance capacity. This study may provide important
      information regarding the need for post-operative antibiotics and prevention of infection in
      this patient group.

      This research will be the first of its kind to address this issue in this vulnerable group of
      patients and no study has ever looked at the effect of transplantation on the immune cells of
      the liver. This study will investigate the ability of the liver to clear particles (albumin
      microspheres) from the blood and will monitor the recover and improvement in function of
      these cells over a period of time.

      Results of any pilot studies

      A study also from the eLISTER group (Edinburgh liver injury in surgery and transplantation
      experimental research) about the effect of major liver resection on innate immunity to
      bacterial endotoxin was approved by Lothian research Ethics Committee LREC/2002/1/31. This
      trial was performed between May 2003 and 2005. This study looked at the adaptive response of
      the reticuloendothelial system to major liver resection. We found a strong correlation
      between clearance of albumin microspheres and ICG (indocyanine green clearance), supporting
      the assertion that hepatocellular function and RES phagocytosis are related if only in terms
      of liver volume. We also demonstrated marked defects in RES phagocytosis in patients with
      chronic liver disease or normal liver function, who had undergone a major liver resection.

      Validation of technique of measurement of phagocytic clearance of Tc-99m labelled (Nanocoll®)
      microaggregated human albumin To determine reticuloendothelial system (RES) phagocytosis
      activity and liver phagocytic function respectively we will measure plasma clearance of 99mTc
      labelled micro-aggregated human albumin without any imaging studies. It has been shown in
      several studies that this is a reliable method to estimate RES phagocytosis activity. By
      measuring the plasma radioactivity disappearance rate instead of doing imaging studies a
      radioactivity dose of less than 15 MBq is sufficient to determine 99mTc plasma clearance
      accurately. Disappearance of 99mTc blood activity will be measured serially at 3-minutes
      intervals to 30 minutes, at 10-minutes intervals to 60 minutes and at 20-minutes intervals to
      120 minutes. Three half-life times required for the 99mTc albumin microspheres counting rate
      to fall from 100% to 50%, from 50% to 25% and from 25% to 12.5% of the value obtained at
      three minutes after injection are noted and the mean half-life and standard deviation,
      expressing the microspheres blood clearance, is calculated. To determine the possibly
      non-linear nature of albumin microspheres clearance over time the area under the curve will
      be calculated over the observation time using integral function. Mean half-life of albumin
      microspheres in the blood and area under the curve at day 1 and day 7 after transplantation
      will be expressed as a percentage of preoperative values and compared between individuals and
      patient groups. We hypothesize that the phagocytosis activity of marginal compared to good
      liver grafts is significantly impaired after liver transplantation due to the decreased
      number of phagocytes as well as due to the decreased synthesis of substances which usually
      facilitates phagocytosis. If this hypothesis is true, the RES phagocytosis activity in the
      marginal grafts should be significantly increased after liver transplantation and should be
      comparable to the RES phagocytosis activity of non-marginal grafts.

      Aims

      This project will test the hypothesis that liver transplantation of normal and marginal
      grafts results in a significant impairment of innate immunity to bacterial endotoxin.

      We intend to characterise the nature or reticuloendothelial clearance impairment following
      liver transplantation and its recovery on marginal and non-marginal grafts. We also wish to
      correlate clearance capacity with measures of hepatocyte injury (ALT/AST) and liver
      dysfunction score to establish whether the two processes are independent or related.

      In this regard we will compare marginal and non-marginal organs and the relationship between
      reticuloendothelial cell dysfunction and cold ischemic time. Reticuloendothelial clearance
      capacity will also be related to evidence of clinical infection in the postoperative course.

      Research questions - Hypotheses

      I. Liver transplantation results in a significant impairment of innate immunity to bacterial
      endotoxin.

      II. The degree of impairment in innate immunity to endotoxin is directly related to the
      functional status of the liver graft. (Patients undergoing liver transplantation with
      non-marginal and marginal grafts will be compared).

      III. To establish whether there is any correlation between liver cell (hepatocyte) injury and
      immune cell (Kupffer cell) injury after transplantation.

      IV. To establish the effect of liver transplantation on serum expression of acute phase
      protein opsonins.
    

Intervention name(s): Nanocoll®
Intervention type(s): Radiation
Intervention description(s): To determine reticuloendothelial system (RES) phagocytosis activity and liver phagocytic function respectively we will measure plasma clearance of 99mTc labelled micro-aggregated human albumin without any imaging studies.
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Patients on the waiting list for liver transplantation will be invited to participate in
        the study and written informed consent will be obtained from each participant. Patients who
        are undergoing transplantation will be studied before operation, 24 hours after
        transplantation and 7 days after transplantation.
      
Keywords: Liver Transplantation; Immunosystem of the Liver; Marginal and Non-marginal grafts