Investigation of hepatocyte signaling pathways in chronic kidney disease : clinical and experimental studies

Abstract: Chronic kidney disease (CKD) is defined as a loss of renal function from any cause and lasting for more than three months. The CKD phenotype is similar across multiple etiologies, suggesting that renal damage itself is a dominant factor. Thus, regardless of the cause even a moderate loss of renal function is associated with impaired hepatic metabolism of glucose, cholesterol, lipid particles, bile acids and plasma proteins. There are surprisingly few studies investigating a putative contribution of this impaired hepatic metabolism to the phenotype of CKD. The overall aim of the current thesis was thus to investigate a hypothetical impact on certain well-characterized hepatic signaling pathways in uremic patients and through both clinical and experimental studies. In Paper I, we describe the release of FGF-19 to the blood, following a meal provocation rich in energy and fat given to CKD patients with severely impaired renal function as well as to age- and gender-matched healthy subjects. We report that the expected increase in postprandial FGF-19 appears to be blunted in CKD patients due to other reasons than delayed gastric emptying. Seven days of pre-treatment with either one of the natural anti-oxidants N-acetylcysteine or anthocyanins led to a partial normalization of postprandial FGF-19 release. In Papers II and III, primary cultures of human hepatocytes were used to study intra-cellular metabolic signaling under uremic conditions in vitro. We designed and used a model entailing culture of these cells (isolated from resected livers) together with CKD patient or healthy sera. We found that hepatocytes exposed to uremic sera rapidly develop an unhealthy metabolism characterized by increased gluconeogenesis and lipogenesis accompanied by perturbations of several key cellular signaling networks. We found no effects of uremic sera on FGF-19 receptor signaling, bile acid synthesis or bile composition. In Paper IV, we investigated the role of hepatic metabolism on systemic FGF-19 levels. Portal and systemic (peripheral arterial and central venous) blood concentrations of FGF-19 and bile acids were assessed in 75 non-CKD patients undergoing liver surgery. We found no differences of FGF-19 concentrations between portal and systemic blood. Furthermore, treatment of primary hepatocytes with FGF-19 in vitro inhibited CYP7A1 expression only at supra-physiological concentrations (2.3-fold decrease) while physiological concentrations of the bile acid CDCA elicited a 12-fold decrease. We conclude that systemic blood concentrations of FGF-19 can be considered to mirror portal concentrations at least in non-CKD populations.