Proteomic Analysis of Protein Plugs: Causative Agent of Symptoms in Patients with Choledochal Cyst

Abstract

Symptoms of choledochal cysts are caused by protein plugs. We performed proteomic analysis of protein plugs to elucidate formation mechanism. Protein plugs were obtained from three pediatric patients with choledochal cyst. Proteins were separated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gel bands common to the samples were excised for mass spectrometry. Mass spectra were compared with the NCBI database for protein identification. Gel bands of protein plug samples were predominant at 14 kilodaltons (kDa), followed by 29 kDa. Four other thin bands were common to the plug samples. Four bands (including 14 and 29 kDa) were identified as lithostathine, and one band as serum albumin. Plugs consisted mostly of lithostathine, a protein secreted by pancreatic acinar cells into pancreatic juice. The mechanism involves trypsinogen and lithostathine regurgitating into the cyst through an aberrant union of pancreaticobiliary ducts. Activated trypsin cleaves soluble lithostathine into insoluble forms that aggregate to form plugs.

Japanese clinical practice guidelines for pancreaticobiliary maljunction

“…The reflux of activating enzymes with strong cytotoxic effects, such as trypsin and phospholipase A2, is regarded as an important factor in the induction of pancreatic damage [81,82]. On the other hand, there are reports suggesting that protein plugs in the common channel may cause transient pancreatic duct obstruction, subsequently inducing pancreatitis [3,82].…”

“…The reflux of activating enzymes with strong cytotoxic effects, such as trypsin and phospholipase A2, is regarded as an important factor in the induction of pancreatic damage [81,82]. On the other hand, there are reports suggesting that protein plugs in the common channel may cause transient pancreatic duct obstruction, subsequently inducing pancreatitis [3,82]. It has been suggested that the hyperamylasemia seen in PBM may not always reflect the onset of acute pancreatitis, but, rather, the hyperamylasemia may sometimes be the result of the leakage of biliary amylase (originally from the pancreatic juices that flow back into the bile duct) into the blood through ''cholangiovenous reflux'', and/or the leakage of pancreatic amylase into the blood through the ''lymphatic pathway'', both being due to a rise in biliary tract pressure [83].…”

“…In PBM, symptoms and signs such as abdominal pain, vomiting, jaundice, and hyperamylasemia arise due to the increases in the pancreatic intraductal pressure and in the biliary tract pressure that result from the obstruction of the common channel or the narrow segment by protein plugs [82,108]. Hyperamylasemia does not really reflect true pancreatitis, but, rather, in most cases it is considered to be the result of pancreatic enzymes flowing back from the bile into the blood through cholangio-venous reflux [83].…”

Endoscopic Therapy for Patients With Pancreaticobiliary Maljunction: A Follow-up Study

“…Further investigation is still necessary. Protein plugs compacted in the common channel are thought to represent the cause of the symptoms and even acute pancreatitis in PBM [15]. The JSPBM guideline mentioned that protein plugs were detected in at least 30 % of pediatric PBM patients [1].…”

“…A dilated common channel was defined by the common channel > 5mm in diameter [1]. Protein plugs, which resulted from the retention of pancreatic juice mixed with bile, were fragile in texture and translucent on cholangiopancreatography [15] (Figure 1). ERCP technical success was assessed based on the intent of the ERCP procedure, which is usually known before the procedure.…”