Introduction Obstruction of the biliary tree has a variety of aetiologies. The correct diagnosis is crucial for appropriate definitive therapy. A major differential diagnosis of biliary obstruction is pancreatic adenocarcinoma (PA). PA is the 10th most common cancer in the UK with mortality similar to incidence. Diagnosis of PA relies on a combination of cross-sectional imaging and serum biomarkers, but only a minority of cases are diagnosed correctly and early enough for curative resection. Earlier diagnostic certainty would be likely to improve outcome and guide therapeutic strategy. Proteomic profiling is a promising technique for new biomarker discovery, but has rarely been successfully carried out in human bile. This project (1) analyses and compares the proteomes of bile from PA patients vs. bile from patients with benign biliary disease and (2) seeks to identify potential protein biomarkers that can differentiate PA from benign biliary disease.
Methods Bile was aspirated at ERCP from patients with benign or malignant biliary obstruction. Particulate matter was removed by centrifugation and equal volumes subjected to SDS-PAGE. In-gel trypsin digestion was performed and the resulting peptides analysed by tandem mass spectrometry. Proteins were identified using SEQUEST to search the human RefSeq protein sequence database. Progenesis software was used to compare relative levels of proteins between patient groups.
Results Proteomic analysis of bile from four patients with PA and four with benign biliary obstruction was performed. Over 100 different proteins were identified, including pancreatic gastric triacylglycerol lipase, carboxypeptidase B and bile salt-activated lipase, confirming that the profile of proteins represents the biliary proteome. Several differentially expressed proteins were identified including upregulation of carcinoembryonic antigen–related cell adhesion molecule 6 (CEACAM6) in the malignant group.
Conclusion This work confirms that bile is amenable to proteomic analysis and that differences in the biliary proteome can be detected in malignant and non-malignant cases. We confirmed earlier reports of CEACAM6 overexpression in PA. We are currently analysing the data further to identify additional candidate biomarker proteins. Future work will extend this approach to the study of bile in other diseases, such as cholangiocarcinoma.
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