The farnesoid X receptor (FXR) controls the synthesis and transport of bile acids (BAs). Mice lacking expression of FXR, designated Fxr-null, have elevated levels of serum and hepatic BAs and an increase in BA pool size. Surprisingly, at 12 months of age, male and female Fxr-null mice had a high incidence of degenerative hepatic lesions, altered cell foci and liver tumors including hepatocellular adenoma, carcinoma and hepatocholangiocellular carcinoma, the latter of which is rarely observed in mice. At 3 months, Fxr-null mice had increased expression of the proinflammatory cytokine IL-1beta mRNA and elevated beta-catenin and its target gene c-myc. They also had increased cell proliferation as revealed by increased PCNA mRNA and BrdU incorporation. These studies reveal a potential role for FXR and BAs in hepatocarcinogenesis.

Pregnane X receptor (PXR) expression was shown to be protective in inflammatory bowel disease (IBD). However, the mechanism by which PXR provides protection remains unclear. Wild-type and Pxr-null mice were treated with the PXR agonist pregnenolone-16alpha-carbonitrile or vehicle and administered 2.5% dextran sulfate sodium (DSS) in drinking water to induce IBD. Typical clinical symptoms were evaluated on a daily basis. In vivo intestinal permeability assays and proinflammatory cytokine analysis were performed. PXR agonist-treated mice were protected from DSS-induced colitis compared with vehicle-treated mice, as defined by body weight loss, diarrhea, rectal bleeding, colon length, and histology. Pregnenolone-16alpha-carbonitrile did not decrease the severity of IBD in Pxr-null mice. PXR agonist treatment did not increase epithelial barrier function but did decrease mRNA expression of several NF-kappaB target genes in a PXR-dependent manner. The present study clearly demonstrates a protective role for PXR agonist in DSS-induced IBD. The data suggest that PXR-mediated repression of NF-kappaB target genes in the colon is a critical mechanism by which PXR activation decreases the susceptibility of mice to DSS-induced IBD.

No abstract

CYP2E1 metabolizes many low-molecular weight toxins and carcinogens. Some in vitro experiments suggest that CYP2E1 may be involved in the metabolic activation of diethylnitrosamine. However, there has been no direct evidence demonstrating a role for CYP2E1 in diethylnitrosamine-mediated carcinogenesis in vivo. To clarify this, we carried out a diethylnitrosamine-induced hepatocarcinogenesis experiment using Cyp2e1-null mice. Male 14-day-old wild-type and Cyp2e1-null mice were treated with diethylnitrosamine (10 mg/kg of body weight) and killed at weeks 24 and 36 after diethylnitrosamine treatment for investigation of tumors and at 6, 24, and 48 h for examination of apoptosis and gene expression. Liver weights of Cyp2e1-null mice were significantly different at weeks 24 and 36 compared with wild-type mice (P < 0.01). Liver tumor incidences of Cyp2e1-null mice were significantly decreased at weeks 24 and 36 compared with wild-type mice (P < 0.01). Cyp2e1-null mice showed significant decrease in the multiplicities of hepatocellular adenoma at weeks 24 and 36 (P < 0.05 and P < 0.01, respectively), and of hepatocellular carcinoma at week 36 (P < 0.01) compared with wild-type mice. Apoptotic index and caspase-3 and/or Bax mRNA expression of Cyp2e1-null mice were significantly different at 6, 24, and 48 h after diethylnitrosamine treatment compared with wild-type mice (P < 0.05). We conclude that Cyp2e1-null mice show lower tumor incidence and multiplicity compared with wild-type mice in diethylnitrosamine-induced hepatocarcinogenesis. It is suggested that CYP2E1 completely participates in diethylnitrosamine-induced hepatocarcinogenesis, and high frequency of tumors in wild-type mice could be associated with the increased apoptosis. [Cancer Res 2007;67(23):11141-6]

Background-Hepatocyte nuclear factor 4α (HNF4α; NR2A1) is an orphan member of the nuclear receptor superfamily expressed in liver and intestine. While HNF4α expression is critical for liver function, its role in the gut and in the pathogenesis of inflammatory bowel disease (IBD) is unknown.

The present study shows that a chronic increase in HIF signaling in the colon epithelial cells initiates a hyperinflammatory reaction that may have important implications in developing therapeutic strategies for inflammatory bowel disease.

To investigate the pathogenic mechanism of ulcerative colitis, a dextran sulfate sodium (DSS)-induced acute colitis model was examined by serum metabolomic analysis. Higher levels of stearoyl lysophosphatidylcholine and lower levels of oleoyl lysophosphatidylcholine in DSS-treated mice compared to controls led to the identification of DSS-elicited inhibition of stearoyl-CoA desaturase 1 (SCD1) expression in liver. This decrease occurred prior to the symptoms of acute colitis and was well correlated with elevated expression of proinflammatory cytokines. Furthermore, Citrobacter rodentium-induced colitis and lipopolysaccharide treatment also suppressed SCD1 expression in liver. Scd1 null mice were more susceptible to DSS treatment than wild-type mice, while oleic acid feeding and in vivo SCD1 rescue with SCD1 adenovirus alleviated the DSS-induced phenotype. This study reveals that inhibition of SCD1-mediated oleic acid biogenesis exacerbates proinflammatory responses to exogenous challenges, suggesting that SCD1 and its related lipid species may serve as potential targets for intervention or treatment of inflammatory diseases.

Arsenic is a well-documented human carcinogen, and contamination with this heavy metal is of global concern, presenting a major issue in environmental health. However, the mechanism by which arsenic induces cancer is unknown, in large part due to the lack of an appropriate animal model. In the present set of experiments, we focused on dimethylarsinic acid (DMA), a major metabolite of arsenic in most mammals including humans. We provide, for the first time, the full data, including detailed pathology, of the carcinogenicity of DMA in male F344 rats in a 2-year bioassay, along with the first assessment of the genetic alteration patterns in the induced rat urinary bladder tumors. Additionally, to test the hypothesis that reactive oxygen species (ROS) may play a role in DMA carcinogenesis, 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in urinary bladder was examined. In experiment 1, a total of 144 male F344 rats at 10 weeks of age were randomly divided into four groups that received DMA at concentrations of 0, 12.5, 50 and 200 p.p.m. in the drinking water, respectively, for 104 weeks. From weeks 97-104, urinary bladder tumors were observed in 8 of 31 and 12 of 31 rats in groups treated with 50 and 200 p.p.m. DMA, respectively, and the preneoplastic lesion, papillary or nodular hyperplasias (PN hyperplasia), was noted in 12 and 14 rats, respectively. DMA treatment did not cause tumors in other organs and no urinary bladder tumors or preneoplastic lesions were evident in the 0 and 12.5 p.p.m.-treated groups. Urinary levels of arsenicals increased significantly in a dose-responsive manner except for arsenobetaine (AsBe). DMA and trimethylarsine oxide (TMAO) were the major compounds detected in the urine, with small amounts of monomethylarsonic acid (MMA) and tetramethylarsonium (TeMa) also detected. Significantly increased 5-bromo-2'-deoxyuridine (BrdU) labeling indices were observed in the morphologically normal epithelium of the groups treated with 50 and 200 p.p.m. DMA. Mutation analysis showed that DMA-induced rat urinary bladder tumors had a low rate of H-ras mutations (2 of 20, 10%). No alterations of the p53, K-ras or beta-catenin genes were detected. Only one TCC (6%) demonstrated nuclear accumulation of p53 protein by immunohistochemistry. In 16 of 18 (89%) of the TTCs and 3 of 4 (75%) of the papillomas, decreased p27(kip1) expression could be demonstrated. Cyclin D1 overexpression was observed in 26 of 47 (55%) PN hyperplasias, 3 of 4 (75%) papillomas, and 10 of 18 (56%) TCCs. As a molecular marker of oxidative stress, increased COX-2 expression was noted in 17 of 18 (94%) TCCs, 4 of 4 (100%) papillomas, and 39 of 47 (83%) PN hyperplasias. In experiment 2, 8-OHdG formation in urinary bladder was significantly increased after treatment with 200 p.p.m. DMA in the drinking water for 2 weeks compared with the controls. The studies demonstrated DMA to be a carcinogen for the rat urinary bladder and suggested that DMA exposure may be relevant to the carcinogenic risk of inorganic arsenic in humans. Diverse genetic...