After liver transplantation, BCS is a serious complication threatening patients, at present the mechanism is not completely clear. The naming of the biliary cast is in a variety, such as biliary sludge, gallstones and bile duct epithelial shedding. The exudative inflammation after bile duct epithelial damage (large leakage of fibrinogen and then formation of cross-linked fibrin) leading to the formation of biliary cast, is a persuasive ratiocination recently raised by the author[7-8], some of the previous biochemical analysis have confirmed the compositions of biliary cast include bilirubin, bile salts and proteins[9], and it is also confirmed in a view of electron microscopy and histological slices that fibrin exists in the biliary cast[10]. So, whether massive proteins bio-information exist in biliary cast, whether the new ratiocination can be verified or a prewarning marker can be found all deserve further investigation.
There is no report addressing the protein analysis of biliary cast at home and abroad, the difficulty of this experiment is also in the handling of specimens. In preliminary experiments, the authors have used 10% HCl solution and 10% NaOH solution to boil biliary cast, respectively, but no dissolution of biliary cast was found. In this experiment, during the procedure of ultrasonic processors, some non-broken fibers were still seen and not easily dissolved, the specific reasons remain un-known yet. Thus the whole protein obtained in this experiment may not be the whole. In the high definition mass spectrometry analysis on biliary cast protein, the authors found that some samples contained special proteins: case 1 containing anti-tetanus toxoid Ig, case 2 containing anti-rabies virus Ig. The accuracy of this experiment has been confirmed through the return visit cases. The type of whole protein is specific in each people body fluids or tissues. To make clear of the reasons for the casting formation, we should find common features. In this study, a common protein is reliable and accurate in the biliary cast through the observation of the whole protein overlapped in 4 specimens, also showing that biliary cast common protein exhibits a very important value on revealing the biliary cast formation mechanism and expanding the following study.
The discovered common protein includes some proteins which are not yet named in the world, its exact function is not clear and this article will not mention. From 4 specimens of common protein finger printing, we found that there are three kinds of fiber proteins (α-fibrinogen precursor, β-fibrinogen precursor, fibrinogen γ-chain), fully explaining a correlation of biliary cast formation with fibrin exudation. The cathepsin G, calcium-binding protein A9 and lactoferrin has been extensively studied in the medical field at recent years, greatly associated with inflammatory reaction in various systems and tissues, the existence of these proteins in the biliary cast also indicates an inflammation of bile duct wall following bile duct epithelial damage, which is consistent with the biliary cast formation mechanism.
Usually cathepsin G refers to the activated lysosomal protease in the acidic environment, belonging to a papain. Cathepsin G plays an important role in the protein degradation, in addition to lysosomes, according to cell type and cell micro-environment, cathepsin G may distributes widely and acts various functions. Beside matrix degradation, it is also involved in growth factor, vascular proliferation regulation and assisting other cytokines regulation, and contributes to cell migration, proliferation and apoptosis. Because of the specificity, cathepsin substrate cab modify and process many elements, leading to their activation and inactivation, plays an important role. Cathepsin G is of great importance on the regulation of stromal vascular proliferation[11-13].
Calcium-binding protein A9 (also S100A9) at relatively small molecular weight (13×103), its expression has a strict specificity, under normal circumstances only granulocytes and monocytes express at the early stages of cell differentiation and in the cycle state in bone marrow, while the macrophages settled in tissues don’t express, under certain conditions such as early stage of inflammation, exudative inflammatory cells express, most of which exhibit S100A9/S100A8 complex. S100A9 is mainly localized in the cytoplasm, also turns to the cytoskeleton and plasma membrane so as to facilitate the accumulation of intracellular calcium[14]. It is suspected that S100A9 is related to wound healing, and its possible mechanism is involved in S100A9 chemotaxis on keratin cytoskeleton reconstruction in epithelial wound and (or) on the inflammatory cells[15-19]. In the cerebral infarction, trauma or cardiac surgery, the serum S100 A9 protein concentration also increases, and it is considered as serum biochemical marker of severe brain injury, plays a certain extent predictive value on minor brain damage[20-21]. Some studies have shown a positive correlation between the rejection reaction intensity and the concentration of S100A9 in serum following kidney transplantation[22].
Lactoferrin is an iron-binding glycoprotein, belonging to transferrin protein family. Lactoferrin can be found in milk and animal body fluids, is a secretion of neutrophils. Recently, many studies have revealed the physiological and biological functions of lactoferrin. Its biological activity includes ion-transfer function; anti-microbial function; anti-fungal activity; anti-viral activity; toxin binding activity; promoting the activity of some animal cells; platelet binding activity; immunomodulatory activity, involved in local secretion immunization together with immune globulin and other protective factors, reducing damage and promoting wound healing[23-30].
Further studies should focus on whether these proteins are expressed in patient’s bile following liver transplantation, and used as a standard for determining the BCS and the inflammatory response after bile duct epithelial damage.
In some cases of severe bile duct necrosis, the matrix metalloproteinases, neutrophil elastase precursor, neutrophil gelatinase-associated lipocalin, Chain A, Crystal Structure of Human Neutrophil Peptide 2, Hnp-2 (Variant Gly16 -> D-Ala) (trypsin-like serine protease) and the Human Cathepsin G expression may be associated with scar formation after biliary epithelial necrosis. Previous studies have confirmed that these enzymes (specific proteins) are involved in the tissue reconstruction following acute inflammation[11]. Therefore these proteins are expected to become a marker of long-term prognosis of BCS.
The proteins exist in biliary cast; the common protein of 4 biliary cast specimens reveals a correlation of biliary cast formation with bile exudative inflammation (fibrin) after bile epithelial damage; some proteins may be used as an marker of prewarning BCS emergence, determining the bile inflammation following bile epithelial damage and the BCS prognosis.
