Research ArticleOxidative albumin damage in chronic liver failure: Relation to albumin binding capacity, liver dysfunction and survival
Introduction
Albumin, a 66.5 kDa protein (Fig. 1), is the most abundant plasma protein, the main determinant of colloid osmotic pressure and an important carrier for endogenous and exogenous substances [1]. Among its most important functions are fatty acid transport (on several binding areas), drug binding and transport, metal chelation, and free radical scavenging which is mediated by the anti-oxidant properties of its thiol moiety at cysteine-34 (reviewed in [2]).
Albumin is the major extracellular source of reduced sulfhydryl groups, which are potent scavengers of reactive oxygen and nitrogen species [3]. Depending on the redox state, there are three major fractions of albumin: human mercaptalbumin (HMA), the non-oxidized form with a free thiol group on cysteine-34, and two different oxidized forms: (i) human non-mercaptalbumin-1 (HNA1) with cysteine, homocysteine or glutathione bound to cysteine-34 by a disulfide bond and (ii) human non-mercaptalbumin-2 (HNA2) with cysteine-34 irreversibly oxidized to sulfinic or sulfonic acid [4], [5]. Oxidative stress is believed to play an important role in advanced liver failure [6] and may be reflected in oxidative modification of albumin. Decreased HMA and/or elevated HNA levels have been reported in chronic liver disease and these changes have been shown to correlate with its severity as estimated by the Child-Pugh score [7], [8]. Recently, we demonstrated a 4-fold increase of the irreversibly oxidized albumin fraction, HNA2, indicating a marked alteration in the redox state of circulating albumin, in patients with advanced liver disease [9].
Albumin harbours two specific binding sites described by Sudlow: site I, which binds large heterocyclic compounds and dicarboxylic acids (such as bilirubin), and site II, which binds aromatic carboxylic compounds (such as benzodiazepines) [10]. Oxidized albumin shows altered binding capacities for several substances used to assess albumin function [11], [12]. Decreased binding of dansylsarcosine – a model ligand for the benzodiazepin binding site II – was found in patients with end-stage liver disease [13], [14]. The pathogenesis of this impaired binding capacity and, specifically, its relation to oxidative albumin damage remain unknown.
Several disturbances of albumin binding function are known to occur in cirrhotic patients [9], [14], [15]. Based on these pathophysiologic changes, albumin infusions are being used therapeutically to normalize the serum albumin level and/or restore albumin function in various conditions such as prevention and treatment of hepatorenal syndrome, prevention of postparacentesis circulatory dysfunction, and extracorporeal albumin dialysis for removal of potentially toxic substances accumulating in liver failure (reviewed in [16]). These beneficial effects are believed to be mediated at least in part by improved toxin binding and transport following infusion of fresh albumin or, in case of albumin dialysis, regeneration of toxin-laden albumin.
Acute-on-chronic liver failure (ACLF), i.e., acute exacerbation of chronic liver failure, is frequently triggered by infection and its clinical features such as end-organ failure resemble those of sepsis [17]. Since ACLF is believed to be mediated by oxidative stress [6], oxidation of albumin is likely to occur. The specific aims of the present study were (i) to assess oxidative modification of albumin in these clinical conditions, (ii) to relate these changes to albumin dysfunction, specifically the disturbance of site II specific binding, and (iii) to determine the prognostic significance of the observed changes in chronic liver failure.
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Patients
The study population comprised 67 consecutive cirrhotic patients hospitalized for acute decompensation at the Medical University of Graz, including 16 patients requiring ICU treatment, and 18 consecutive non-cirrhotic patients with sepsis without evidence for cirrhosis or underlying hematologic disease admitted at our ICU. In addition, 15 age- and sex-matched blood donors served as healthy controls. Patients with hepatocellular carcinoma, recent gastrointestinal bleeding (<7 days before
Results
The characteristics of the study population including the external validation set are shown in Table 1. Within the cirrhosis cohort, the main reasons for admission were ascites (40%), acute kidney injury (22%), gastrointestinal bleeding (19%), and hepatic encephalopathy (8%). As expected, both in cirrhotic and septic patients, bilirubin and CRP were increased and albumin decreased compared to controls. Septic patients presented with the highest leukocyte counts and CRP values while bilirubin
Discussion
In the present study, we observed marked alterations of the redox state of albumin and significant impairment of albumin binding capacity (site II) in patients with chronic liver failure as well as in septic patients without liver failure. This is in line with our previous finding of decreased binding of bilirubin to the oxidized albumin fractions, HNA1 and HNA2 [9]. Univariate analysis showed correlations of DS binding with liver functions parameters as well as HNA2 in cirrhotic but not in
Financial support
This study was supported by the Franz Lanyar Stiftung (project # 314) and by BioPersMed (COMET K-project 825329), which is funded by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT) and the Austrian Federal Ministry of Economics and Labour/the Federal Ministry of Economy, Family and Youth (BMWA/BMWFJ) and the Styrian Business Promotion Agency (SFG).
V.S. was the recipient of an Erwin-Schrödinger fellowship (J2547) from the Austrian Science Foundation.
Conflict of interest
The authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.
Acknowledgements
The technical assistance of Martina Brtnik, Doris Payerl, and Stefan Spoerk is gratefully acknowledged.
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