Native liver fibrosis in biliary atresia : From pathobiology to clinical outcomes

Background. Biliary atresia (BA) is a destructive, obliterative fibroinflammatory cholangiopathy of infancy, affecting around 1 in 20 000 newborns a year. Despite successful surgical restoration of bile flow by portoenterostomy (PE), liver fibrosis progresses into liver failure and the need for liver transplantation (LTx) before adulthood in most patients. Pathogenesis underlying progressive liver fibrosis after successful PE is unclear. Aims. The aim of this study was to investigate the molecular mechanisms underlying persistent liver fibrogenesis after successful PE and to address the predictors of outcomes. Patients and methods. Three cross-sectional studies investigated gene and protein expression of liver biopsies and serum levels of profibrogenic growth factors, proinflammatory cytokines and extracellular matrix mediators from 25–28 BA patients treated in Helsinki University Hospital between 1991 and 2013, taken at PE and over three years of follow-up after successful operation. The change in survival rates before and after centralization and predictive values were analyzed in BA patients treated in Helsinki between 1987 and 2016 (n=61). Results. During three years following successful PE, serum bilirubin levels remained low [median 10 (interquartile range 4–17) µmol/L]. Despite the resolution of histologic cholestasis and reduction in inflammation, liver fibrosis persisted. Ductular proliferation prevailed and periportal hepatocyte cytokeratin 7 immunopositivity, indicating hepatocyte-to-cholangiocyte metaplasia, increased. If clearance of jaundice (COJ) was not achieved, both histologic cholestasis and inflammation persisted, and progression of liver fibrosis was faster. Of the matrix metalloproteinases (MMPs) studied, MMP-7 was uniquely upregulated in BA when compared to both non-fibrotic and fibrotic control biopsies at protein, gene and serum levels. MMP-7 localized to the biliary epithelium and was related to liver fibrosis stage. Serum MMP-7 showed significant predictive value for portal fibrosis after successful PE. Protein expression of collagen 1, alfa-smooth muscle actin (α-SMA, indicator of activated myofibroblasts), transforming growth factor-beta (TGF-β)-1 and TGF-β2 were all increased at PE and at follow-up compared to non-fibrotic controls. After successful PE, protein expression of TGF-β1, but not that of TGF-β2, decreased. Expression of TGF-β1 and TGF-β2 correlated with Metavir fibrosis stage. Gene expression of platelet-derived growth factor (PDGF) was elevated compared to fibrotic and non-fibrotic controls. Gene expression of proinflammatory cytokines was decreased or comparable when compared to controls. After the centralization of treatment in Helsinki (2005), the median caseload increased from 1 to 3–4 per year. There was an increase in COJ rate from 42% to 80%, a five-year native liver survival from 38% to 70%, and a five-year overall survival rate from 68% to 94%. In multivariate analysis, the only predictor of COJ was high-grade portal inflammation at PE, and the normalization of bilirubin within 3 months predicted native liver survival. Conclusions. After successful PE, a molecular signature of active fibrogenesis prevails, while histologic portal inflammation and expression of proinflammatory cytokines decreases. An increased hepatic expression of MMP-7 is unique to BA and offers a potential follow-up and therapeutic target to extend native liver survival after COJ. TGF-β2 and PDGF might be essentially involved with BA liver fibrogenesis after cholestasis has resolved.