The activation of NF-kB, Pregnane X Receptor, and Constitutive Androstane Receptor is modulated by the degree of cholestasis

Introduction: NF-kB is known to be activated in the early stages of cholestasis, acting a reduction of liver injury. Pregnane X Receptor (PXR) and Constitutive Androstane Receptor (CAR) are two nuclear receptors (NRs) that regulate bile acid metabolism and transport. A mutual negative crosstalk between NF-kB and NRs has been reported, but conflicting data are available on the impact of their relationship in cholestasis. Aim: To analyse the changes in activation of NF-kB, PXR, and CAR in an experimental model of cholestasis. Methods: Cholestasis was induced in 8 male Wistar rats by bile duct ligation; 4 sham-operated rats were used as controls. The degree of cholestasis was defined on the basis of histologic examination of liver sections and serum concentration of albumin, ALT, GGT, bilirubin. Activation of PXR, CAR and NF-kB was evaluated by Western blot analysis on nuclear liver fractions. Results: A 2-fold increase in activation of NF-kB was observed in early stage of cholestasis (p < 0.05 with respect to Sham), whereas the nuclear translocation of NF-kB was completely abolished in the late stage (p < 0.001). A significant increase in PXR activation was observed in late stage of cholestasis compared with both early stages and controls (2- and 1.5-fold, p < 0.01 and 0.05, respectively). CAR nuclear expression was 3.4-fold higher in early cholestatic rats than in controls (p < 0.001), whereas CAR activation was virtually abolished when cholestasis became severe (p < 0.05 and p < 0.001 vs. sham and early-stage cholestatic rats, respectively). Conclusions: We provided new evidences of the strict relationship between NRs and NF-kB activation, suggesting a different effect of NF-kB on PXR and CAR activation, which is dramatically enhanced in severe cholestasis. Therefore, a different modulation of the NF-kB pathway by acting on PXR and CAR according to the degree of cholestasis may be considered as a new therapeutic strategy