Antibiotic treatments have been used to modulate intestinal bacteria and investigate the role of intestinal bacteria on bile acid (BA) homeostasis. However, knowledge on which intestinal bacteria and bile acids are modified by antibiotics is limited. In the present study, mice were administered various antibiotics, 47 of the most abundant bacterial species in intestine, as well as individual BAs in plasma, liver, and intestine were quantified. Compared to the two antibiotic combinations (vancomycin+imipenem and cephalothin+neomycin), the three single antibiotics (metronidazole, ciprofloxacin and aztreonam) have less effect on intestinal bacterial profiles, and thus on host BA profiles and mRNA expression of genes that are important for BA homeostasis. The two antibiotic combinations decreased the ratio of Firmicutes to Bacteroidetes in intestine, as well as most secondary BAs in serum, liver and intestine. Additionally, the two antibiotic combinations significantly increased mRNA of the hepatic BA uptake transporters (Ntcp and Oatp1b2) and canalicular BA efflux transporters (Bsep and Mrp2), but decreased mRNA of the hepatic BA synthetic enzyme Cyp8b1, suggesting an elevated enterohepatic circulation of BAs. Interestingly, the two antibiotic combinations tended to have opposite effect on the mRNAs of most intestinal genes, which tended to be inhibited by vacomycin+imipenem but stimulated by cephalothin+neomycin. To conclude, the present study clearly shows that various antibiotics have distinct effects on modulating intestinal bacteria and host BA metabolism.

Taken together, these data indicate that hepatocyte to BE transdifferentiation is regulated by HGF and EGF receptors and that PI3 kinase-mediated signaling independent of AKT is a crucial component of the transdifferentiation process.

The obesity epidemic in industrialized countries is associated with increases in cardiovascular disease (CVD) and certain types of cancer. In animal models, caloric restriction (CR) suppresses these diseases as well as chemical-induced tissue damage. These beneficial effects of CR overlap with those altered by agonists of nuclear receptors (NR) under control of the fastingresponsive transcriptional co-activator, peroxisome proliferator-activated co-activator 1␣ (PGC-1␣). In a screen for compounds that mimic CR effects in the liver, we found statistically significant overlaps between the CR transcript profile in wild-type mice and the profiles altered by agonists of lipid-activated NR, including peroxisome proliferator-activated receptor ␣ (PPAR␣), liver X receptor, and their obligate heterodimer partner, retinoid X receptor. The overlapping genes included those involved in CVD (lipid metabolism and inflammation) and cancer (cell fate). Based on this overlap, we hypothesized that some effects of CR are mediated by PPAR␣. As determined by transcript profiling, 19% of all gene expression changes in wild-type mice were dependent on PPAR␣, including Cyp4a10 and Cyp4a14, involved in fatty acid -oxidation, acute phase response genes, and epidermal growth factor receptor but not increases in PGC-1␣. CR protected the livers of wild-type mice from damage induced by thioacetamide, a liver toxicant and hepatocarcinogen. CR protection was lost in PPAR␣-null mice due to inadequate tissue repair. These results demonstrate that PPAR␣ mediates some of the effects of CR and indicate that a pharmacological approach to mimicking many of the beneficial effects of CR may be possible.

No abstract

Transcription factors are major determinants of cell-specific gene expression in all cell types. Studies in rodent liver have shown that alterations in transcription factor expression determine lineage specification during fetal liver development and signify transdifferentiation of cells of the biliary compartment into 'oval' cells and eventually hepatocytes in adult liver. We examined the cellular localization of hepatocyte-or BEC-associated transcription factors in human fetal and adult liver and in diseases in which transdifferentiation between hepatocytes and biliary cells may play a role. In the normal adult human liver, hepatocyte nuclear factor (HNF)4a and HNF6 appeared exclusively in hepatocytes; HNF1b, HNF3a, and HNF3b were observed only in BEC. During fetal development both BEC and hepatocytes expressed HNF3a, HNF3b, and HNF6. HNF1a was expressed only in fetal hepatocytes. We further examined expression of transcription factors in massive hepatic necrosis and in specific types of chronic liver disease. Hepatocyte-associated transcription factors HNF4a and HNF6 also appeared in BEC in massive hepatic necrosis and chronic hepatitis C virus infection. Similarly, HNF3b that is expressed only in BEC in normal adult liver was also observed in hepatocytes in primary biliary cirrhosis and chronic biliary obstruction. These data mimic previous findings in rodents in which hepatocyte-associated transcription factors appear in biliary cells prior to emergence of oval cells, which function as progenitor cells for hepatocytes when the regenerative capacity of the latter is compromised.