The frequency of liver disease in humans with cystic fibrosis (CF) (focal biliary fibrosis leading to multilobular cirrhosis) ranges up to 43%, with prevalence increasing with age. Multilobular cirrhosis manifesting clinically with portal hypertension has become the third leading cause of morbidity and premature death in CF, and when pulmonary disease is controlled with or without lung transplantation, liver disease is the leading cause of death. The etiology, mechanisms and pathogenesis of CF liver disease are unknown, and currently ursodeoxycholic acid is prescribed without compelling evidence of its efficacy. Extending preliminary studies from this laboratory, the ?F508 and G551D murine models of CF and wild-type (WT) mice will be studied: 1) to explore the hepatobiliary secretory abnormalities of pH, bilirubins, electrolytes and biliary lipids utilizing biophysical, pathophysiological and physical-chemical approaches; 2) to determine the pathogenesis of enteric hyperbilirubinbilia and to correlate this with ileal pH abnormalities, bile salt malabsorption, hepatic bile pH and liver disease; 3) to elucidate the pathophysiology of bile salt malabsorption as a cause of induced enterohepatic cycling of unconjugated bilirubin (UCB), focusing on the ileal bile salt transporter and its response to less alkaline lumenal pH; in addition, to study intestinally hCFTR-rescued CF mice to verify the molecular nature of the intestinal defect; 4) to image and quantify age and gender-related liver histology and ultrastructural studies to detect deposits of metal bilirubinates intraductally and in biliary epithelial cells using transmission and scanning electron microscopy coupled with atomic emission spectroscopy, and to quantify the pathobiology of UCB-induced periductal inflammation, fibrogenesis and obliterative cholangitis; 5) to prevent and treat chronic liver disease of CF mice by a) targeting the biliary tree with norUDCA to increase pH of hepatic bile, b) targeting UCB formation and absorption in the distal gut by non-absorbed polymers with covalently linked D-glucaro-1,4-lactone or cholic acid, and c) targeting bile salt malabsorption using colesevelam HCI to prevent solubility of UCB or by normalizing the lumenal pH using amiloride, a carbonic anhydrase agonist, or by upregulating ASBT activity with budesonide. The molecular insights from these hypothesis-driven specific aims should provide data, molecular understanding and agents that are translatable to humans with CF and lead to new modalities for prevention and treatment of CF liver disease. [unreadable] [unreadable]