T1181 Helicobacter pylori Infection Induces Gastric Mutations in Mice: Influence of Gender and Duration of Infection

The nuclear receptor constitutive androstane receptor (CAR) regulates the expression of enzymes involved in endobiotic and xenobiotic metabolism. CAR is essential for liver tumor promotion by phenobarbital, a prototype tumor promoter of mice. The mechanism by which chronic microbial infection influences tumor progression is unknown. However, previous studies have suggested a role of endobiotics including certain bile acids in tumor promotion. We investigated the mechanism of liver tumor promotion by Helicobacter hepaticus (Hh), the prototype carcinogenic bacterium of mice. Twenty two CAR-/(KO) and 23 CAR+/+ (wild-type, WT) male mice (C3H/HeN) received a single intraperitoneal injection of the genotoxic carcinogen diethylnitrosamine (DEN) at 5 weeks of age. Another group consisting of 21 KO and 20 WT male mice did not receive DEN. The two groups (with and without DEN) were subsequently stratified into four subgroups (two KO and two WT) and orally inoculated with either Hh or sterile media at 8 weeks of age. Mice were euthanized at 50 weeks postinoculation, complete necropsies were performed, and samples were collected for histopathological, microbiological, molecular, and biochemical analyzes. Hepatic Hh colonization as well as hepatic expression of selected nuclear receptors, cytokines, and innate immune mediators were measured by real-time quantitative PCR. The serum concentrations of selected mono-, di-, and tri-hydroxylated bile acids were measured by liquid chromatography tandem mass spectrometry. Chronic infection with Hh induced hepatitis in WT and KO mice with or without DEN. However, relative to Hh-infected WT mice with DEN, Hhinfected KO mice with DEN exhibited the following statistically significant differences: Increased number of liver lobes with dysplasia/neoplasia (P<0.0001), increased multiplicity of liver tumors (P<0.004), decreased Hh colonization in the liver (P<0.04), increased hepatic expression of genes for vitamin D receptor (Vdr) (P<0.04) and cathelicidin antimicrobial peptide (Camp) (P<0.02), and increased serum concentration of chenodeoxycholic acid (P<0.01). Our findings suggest a mechanism of microbial tumor promotion involving increased systemic bile acid concentration and induction of an innate antimicrobial response against bacterial colonization.