Expression of aminopeptidase N in bile canaliculi: A predictor of clinical outcome in biliary atresia and a potential tool to implicate the mechanism of biliary atresia

Background. Only a few studies on extrahepatic biliary atresia (BA) have reported that the morphological changes of bile canaliculi could predict the clinical outcome after portoenterostomy and provide differential diagnosis of neonatal jaundice. Aminopeptidase N (APN) is an ectoenzyme of bile canaliculi that is involved in bile secretion. In this study, we tried to see whether APN of bile canaliculi had a significant role in BA. Patients and methods. We used monoclonal antibody 9B2 to compare the expression of APN in livers with BA, neonatal hepatitis, and choledochal cysts, as well as in nontumorous portions of pediatric hepatic livers with tumors. The expression of APN in fetuses, preterm babies, and term neonates was also studied. Results. A high degree of 9B2 expression in BA was closely related to poor outcome. Cholestasis in choledochal cysts, rather than neonatal hepatitis, made 9B2 expression stronger. Increasing expression of 9B2 from fetuses to neonates was noted and the degree of 9B2 expression was similar between term neonates and nontumorous portions of pediatric livers with tumors. Interestingly, some cases of BA had 9B2 expression like that of preterm babies. Conclusions. APN of bile canaliculi progressively develops from fetuses to neonates and is well developed in neonates. APN can be induced to stronger expression by obstructive jaundice. The amount of expression of APN of bile canaliculi in BA is a predictor of clinical outcome and may be a tool for implicating the mechanism of BA.