Characterization of the content of occluded biliary endoprostheses.

In an attempt to establish why biliary endoprostheses clog we analysed the contents of 21 occluded endoprostheses. The major components of the endoprosthesis sludge were protein (25%) and an insoluble residue (20%) which consisted mainly of plant fibers. Compared with bile the material was also rich in unconjugated bilirubin, while the major components of bile--bile acids and lecithin--accounted for only 15%. Although the sludge often contained some cholesterol crystals, no cholesterol gallstones or pigment or mixed stones were found. The material contained bacteria, but not in abundance. Scanning electron microscopy of the walls of clogged endoprostheses revealed adherence of amorphous material, probably protein. SDS-polyacrylamide gel electrophoresis of the protein fraction of the material from different endoprostheses showed a characteristic pattern. The material always contained two major bands of approximately 16 and 13 kDalton, which were not observed in corresponding bile samples. The 16 and 13 kDalton proteins bound most avidly to the endoprosthesis wall. We postulate that the initial phase in the clogging process is adsorption of proteins, after which other materials such as bacteria, fibers from food and unconjugated bilirubin bind to the wall of the endoprosthesis.