Study of the Mechanisms of Biliary Stent Occlusion: an Analysis of Occluded and Nonoccluded Stents, with Emphasis on the Role of Antinucleating Biliary Anionic Peptide Factor.

Background and Study Aims: Plastic stents tend to become occluded by sludge deposition, and the mechanisms underlying the process are still partly unclear. In the present study, occluded and nonoccluded stents were examined in order to clarify the role of proteins (with emphasis on the 7-kDa biliary antinucleating anionic peptide factor, APF), microorganisms, and minerals.Patients and Methods: In a prospective study comparing stents exchanged prophylactically or in case of dysfunction, 58 polyethylene stents were collected and analyzed. The stents were classified macroscopically as either nonoccluded or occluded. Infrared spectroscopy of the stent contents, 15 % sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), immunological detection and quantification of APF, electron-microscopic scanning, and bacteriological analysis were carried out.Results: Thirty-eight stents were occluded and 20 were patent. The composition of the stent biofilms identified on spectrophotometry differed significantly between occluded and nonoccluded stents (P < 0.01). The main constituent of the biofilm in the occluded stents was calcium bilirubinate and palmitate, but in the nonoccluded stents the main constituent was proteins. The protein spectra did not differ between the two groups. In both groups, the majority of bacterial strains were not positive for beta-glucuronidase. APF contributed to the protein biofilm in all of the stents to a small extent. A significant decrease (- 11.8 %; P < 0.05) in APF was observed in the occluded stents, as evidenced by electrophoresis, immunoblotting, and enzyme-linked immunoassay.Conclusions: Obstruction is initiated by the deposition of a protein biofilm on the inner stent wall; reduced APF levels may play a significant role in this process. Future trials of prophylactic treatment against stent obstruction should be aimed at preventing protein deposition and at modifying the overall balance of protein constituents.