Hepatic Deletion of X-Box Binding Protein 1 in FXR Null Mice Leads to Enhanced Liver Injury.

FXR regulates bile acid metabolism, and FXR null (Fxr-/-) mice have elevated bile acid levels and progressive liver injury. The inositol-requiring enzyme 1α/X-box binding protein 1 (XBP1) pathway is a protective unfolded protein response pathway activated in response to endoplasmic reticulum stress. Here, we sought to determine the role of the inositol-requiring enzyme 1α/XBP1 pathway in hepatic bile acid toxicity using the Fxr-/- mouse model. Western blotting and quantitative PCR analysis demonstrated that hepatic XBP1 and other unfolded protein response pathways were activated in 24-week-old Fxr-/- compared with 10-week-old Fxr-/- mice but not in WT mice. To further determine the role of the liver XBP1 activation in older Fxr-/- mice, we generated mice with whole-body FXR and liver-specific XBP1 double KO (DKO, Fxr-/-Xbp1LKO) and Fxr-/-Xbp1fl/fl single KO (SKO) mice and characterized the role of hepatic XBP1 in cholestatic liver injury. Histologic staining demonstrated increased liver injury and fibrosis in DKO compared with SKO mice. RNA sequencing revealed increased gene expression in apoptosis, inflammation, and cell proliferation pathways in DKO mice. The proapoptotic C/EBP-homologous protein pathway and cell cycle marker cyclin D1 were also activated in DKO mice. Furthermore, we found that total hepatic bile acid levels were similar between the two genotypes. At age 60 weeks, all DKO mice and no SKO mice spontaneously developed liver tumors. In conclusion, the hepatic XBP1 pathway is activated in older Fxr-/- mice and has a protective role. The potential interaction between XBP1 and FXR signaling may be important in modulating the hepatocellular cholestatic stress responses.

Mechanisms of liver injury in high fat sugar diet fed mice that lack hepatocyte X-box binding protein 1.

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of liver diseases in the United States and can progress to cirrhosis, end-stage liver disease and need for liver transplantation. There are limited therapies for NAFLD, in part, due to incomplete understanding of the disease pathogenesis, which involves different cell populations in the liver. Endoplasmic reticulum stress and its adaptative unfolded protein response (UPR) signaling pathway have been implicated in the progression from simple hepatic steatosis to nonalcoholic steatohepatitis (NASH). We have previously shown that mice lacking the UPR protein X-box binding protein 1 (XBP1) in the liver demonstrated enhanced liver injury and fibrosis in a high fat sugar (HFS) dietary model of NAFLD. In this study, to better understand the role of liver XBP1 in the pathobiology of NAFLD, we fed hepatocyte XBP1 deficient mice a HFS diet or chow and investigated UPR and other cell signaling pathways in hepatocytes, hepatic stellate cells and immune cells. We demonstrate that loss of XBP1 in hepatocytes increased inflammatory pathway expression and altered expression of the UPR signaling in hepatocytes and was associated with enhanced hepatic stellate cell activation after HFS feeding. We believe that a better understanding of liver cell-specific signaling in the pathogenesis of NASH may allow us to identify new therapeutic targets.

Mechanistic considerations of photosensitized transformation of microcystin-LR (cyanobacterial toxin) in aqueous environments.

Microcystin-LR (MC-LR), one of the most common cyanotoxins, is produced by harmful cyanobacteria. The current study focuses on the photosensitized transformation of MC-LR in dissolved organic matter (DOM) enriched solutions under solar simulated irradiation. It appears that the direct energy transfer of triplet excited state DOM with MC-LR plays a key role and leads to photosensitized isomerization of Adda side chain. Furthermore a micro-heterogeneous mechanism has been proposed. Size exclude chromatograph (SEC) has been applied to explore the adsorption of MC-LR on the DOM. The adsorption phenomenon supported the fact that the pseudo first-order photodegradation rates showed positive correlation with the adsorption. The photo-transformation rate of MC-LR increases as pH decreases which is also the result of the adsorptive interaction of MC-LR with DOM. Finally two bulk water parameters (TOC and UV350 nm) have been applied to predict the photodegradation rates of MC-LR in the varied water matrixes.

Photochemical transformation of terbutaline (pharmaceutical) in simulated natural waters: degradation kinetics and mechanisms.

In this study, varied nature organic matter isolates were employed to investigate the indirect photo transformation of terbutaline, which is a major feed additive medicine to increase the proportion of lean meat in the livestock. In the indirect photolysis of terbutaline under solar simulated irradiation, (1)O2 plays an important role among the •OH and (3)DOM*. The reaction rate constant of (1)O2 was determined as (7.1 ± 0.3) × 10(6) M(-1) s(-1) at pH 7.0, while the reaction rate constant of •OH was (6.87 ± 0.43) × 10(9) M(-1) s(-1). The contribution of singlet oxygen to the indirect photolysis of terbutaline (19-44%) was higher than that of the hydroxyl radical (1-7%). The pseudo first order rate constants for the photodegradation of terbutaline increase with increasing pH, which indicates that pH mainly affects the reaction rate of the singlet oxygen with the phenolic part of the terbutaline. The Quinone was identified as the main photosensitized product through LC-MS/MS analysis. It is also proposed that the degradation pathway of terbutaline involves reaction between the phenolic part of terbutaline and singlet oxygen. This finding strongly suggests that singlet oxygen was important factor for the photodegradation of terbutaline in natural waters.