Fucosylated Glycoproteins as Markers of Liver Disease

259 Disease Markers 25 (2008) 259–265 IOS Press Fucosylated glycoproteins as markers of liver disease Anand Mehta∗ and Timothy M. Block Drexel University College of Medicine, Department of Microbiology and Immunology, Drexel Institute for Biotechnology and Virology, 3805 Old Easton Road, Doylestown, PA 18902, USA Tel.: 215 489 4905; Fax: 215 489 4920 Abstract. Changes in N-linked glycosylation are known to occur during the development of various diseases. For example, increased branching of oligosaccharides has been associated with cancer metastasis and has been correlated to tumor progression in human cancers of the breast, colon and melanomas. Increases in core fucosylation have also been associated with the development of hepatocellular carcinoma (HCC). Recently, changes in both the total serum glycome and the glycosylation of specific IgG molecules have been observed in people with liver fibrosis and cirrhosis. The mechanisms by which changes in glycosylation are observed and their use as biomarkers of disease will be discussed. Keywords: Hepatitis B virus, Hepatitis C virus, fucosylation, liver fibrosis, liver cancer 1. Introduction Infection of the liver with hepatitis B virus (HBV) and/or hepatitis C virus (HCV) is characterized by the ability to cause either acute infection that is frequently clinically inapparent or an unresolved, long term, chronic infection [1,2]. 10–40% of those chronically infected will develop either liver cirrhosis and/or primary hepatocellular carcinoma (HCC). Cirrhosis is a chronic disease of the liver where the normal liver architecture is replaced by fibrotic scar tissue, and is associated with an eventual decline of liver function. The development of cirrhosis is a pre-malignant condition and leads to an increased risk for the development of HCC [3–5]. Although there are many causative agents for cirrhosis, chronic viral infections of the liver by HBV and/or hepatitis C virus HCV are among the most common etiologies. HCC is a cancer arising from the liver and is referred to as primary liver cancer. HCC is the fifth most common cancer in the world and is the 3rd leading cancer killer worldwide [6].The World Health Or∗ Corresponding author. E-mail: . ganization (WHO) estimated that in 2005 there were 560,000 new cases of liver cancer worldwide, and a similar number of patients died as a result of this disease (http://www.who.int/en). The low survival rates have been attributed to the late diagnosis and poor therapeutic options [7]. 2. Methods for detecting liver disease For HBV and/or HCV infected patients, treatment decisions are based upon biochemical laboratory data, specifically hepatic transaminases, and more importantly the degree of hepatic inflammation and fibrosis on histological analysis [8]. For example, in individuals with HBV, advanced fibrosis and cirrhosis are considered justifications to begin antiviral therapy [4,8,9]. More importantly, the determination of hepatic fibrosis is critical to stage the severity of the liver disease in order to determine the prognosis and response to antiviral therapy [10]. It is thus extremely important to be able to determine the presence of significant fibrosis and cirrhosis in a manner that will allow for routine clinical monitoring. ISSN 0278-0240/08/$17.00  2008 – IOS Press and the authors. All rights reserved 260 A. Mehta and T.M. Block / Fucosylated glycoproteins as markers of liver disease The gold standard for the staging of chronic liver disease is histopathological analysis, especially the determination of the amount of hepatic fibrosis [11]. The degree of liver injury in patients with chronic viral hepatitis is measured using a grading and staging system that are used to measure the degree of inflammation and fibrosis [12]. These are histological indicators that are classically associated with severity and progression of liver disease. However, biopsy is expensive, variable, and has low patient acceptance due to its inherent discomfort and potential risk for serious adverse outcomes. In addition, there is low concordance with the interpretation of the biopsy even among expert pathologists and suffers from sampling error, thereby, giving misleading results [13]. Alternative non-invasive tests for the measurement of hepatic fibrosis are urgently needed. Since the liver is a highly secretory organ, it has been reasoned that the circulation would contain selective molecules that, in their abundance or modification, would reflect the physiological state of the liver. The progression of liver disease into liver cancer is monitored primarily by the use of serum levels of the oncofetal glycoprotein, alpha-fetoprotein (AFP), which is thought to be produced by transformed liver cells. However, AFP can be produced under many circumstances, including other liver diseases [14–16], and is not a definitive marker for the development of HCC. Analysis of the regulatory mechanisms of increased AFP synthesis in hepatic injury and in malignant transformations has been unable to distinguish elevation of AFP between HCC and chronic liver disease [17,18]. Hence the usefulness of AFP screening is limited and its use as a primary screen for HCC has been questioned [4]. 3. Changes in glycosylation associated with HCC The literature indicates that changes in glycosylation occur during the development of HCC. The most notable change is an increase in the level of core alpha 1,6 linked fucosylation of AFP [19,20]. In HCC and in testicular cancer, the glycosylation of AFP shifts from a simple biantennary glycan to an alpha 1,6 linked core fucosylated biantennary glycan. This change has been observed by both direct glycan sequencing of AFP and by increased reactivity of AFP with a variety of lectins that preferentially bind to fucose containing glycan [21]. The species of AFP that reacts preferentially with the lectin lens culinaris (LCH) is referred to as AFP-L3. Several reports have clearly indicated that AFP-L3 is a more specific marker of HCC than is the total AFP protein level [22–24]. Indeed, AFP-L3, gained approval from the US Food and Drug administration (FDA) in 2005 as the only diagnostic assay for HCC. In addition to the increases in fucosylation observed on AFP, other changes in N-linked glycosylation have also been observed. These change include the addition of bisecting N-Acetylglucosamine (GlcNAc) residues along with increased alpha 2,6 linked sialation [25]. These changes have been observed on a more global scale, rather than through the examination of a single glycoprotein. Although the molecular mechanism of increased fucosylation in HCC is not clear [26–28], it is known that the increase is not restricted to AFP [29–31]. Results from several groups have indicated that other liver derived glycoproteins such as serotransferrin, and alpha 1 antitrypsin also become fucosylated with the development of HCC and a recent study has proposed that these glycoforms may be valuable bio (...truncated)