Experimental Helicobacter pylori infection in an animal model
Sammanfattning: Background: Helicobacter pylori is a microaerophilic Gram-negative bacterium colonizing the human stomach. The prevalence of this infection is between 20-90% depending on geographic location. Comprehensive studies have shown significant relationships between H. pylori infection and chronic gastritis, peptic ulcer and gastric carcinoma. The mechanisms behind these associations are still unclear in many aspects. The objective of this thesis was to elucidate some pathogenetic aspects of H. pylori infection based on an animal model using Mongolian gerbils.Aims: To determine bacterial profiles in the stomach of gerbils with and without H. pylori infection. To study the long-term morpho-functional development of H. pylori-induced gastritis. To investigate the gastric mucosal barrier function and to explore the effects of dietary antioxidant vitamin supplements on H. pylori-associated chronic gastritis.Methods and results: Mongolian gerbils were inoculated with H. pylori ATCC 43504 or culture broth (controls). The animals were killed at scheduled time points. The gastric microflora was profiled and identified by temporal temperature gradient gel electrophoresis (TTGE), cloning and pyrosequencing of 16S rDNA variable V3 region. TTGE and pyrosequencing revealed the presence of a mixed bacterial flora in the stomach of both H. pylori infected and control animals. In both cases, lactobacilli appeared to prevail. In H. pylori-infected gerbils, serum concentrations of anti-H. pylori IgG and gastrin increased over time. Mucosal epithelial proliferation quantified after immunohistochemical labeling with 5-bromo-2'-deoxy-uridine was increased in the antrum in short-term gastritis, followed by an increase in the corpus in the long-term. Gene expression of pro-inflammatory cytokines was quantitated by real-time RT-PCR. Interleukin-1beta and tumor necrosis factor-alpha expression was increased in H. pylori-infected gerbils. Beta-actin was not a reliable endogenous control for relative quantitative RT-PCR. Histological parameters of gastritis were semiquantitatively assessed and expressed as a "gastritis score". Gastritis scores increased over time and reached a peak 32 weeks after inoculation. With time there was an expansion of gastritis from the antrum to the corpus. Severe inflammation, ulcer development and pseudopyloric metaplasia (glandular atrophy) were characteristic features. Gastric mucosal samples were mounted in Ussing chambers and 51Cr-EDTA (paracellular probe) and horseradish peroxidase (HRP, protein antigen) were used as indicators of gastric mucosal barrier function. Short-term gastritis showed increased mucosal permeability to 51Cr-EDTA in the antrum. Long-standing gastritis was associated with increased 51Cr-EDTA permeation in both the antrum and corpus and an increased HRP flux in the antrum. In the vitamin supplement study, concentrations of 3-nitrotyrosine (nitrosative protein damage) and thiobarbituric acid reactive substances (TBARS) (oxidative lipid damage) in the gastric mucosa were determined with an immunodot blot and a fluorometric method, respectively. Mucosal concentrations of carbonyl carbons on proteins (oxidative protein damage) and 8-hydroxydeoxyguanosine (oxidative DNA damage) were determined by ELISA. Vitamin supplements had no effect on the colonization with H. pylori. Vitamin C as well as vitamin E supplements reduced mucosal 3-nitrotyrosine concentrations to normal levels in the infected animals. Vitamin E supplement induced decreased mucosal protein carbonyls and TBARS in short-term gastritis. In addition, vitamin C supplement caused attenuated mucosal oxidative DNA damage and milder mucosal inflammation in short-term gastritis.Conclusions: Lactobacilli, the prevailing indigenous bacterium in the stomach of gerbils, may have a probiotic impact on the colonization of H. pylori. The long-term morpho-functional development in the stomach of H. pylori-infected Mongolian gerbils resembles that of H. pylori-infected humans. H. pylori-induced gastritis in gerbils is associated with a long-standing gastric mucosal barrier dysfunction, which follows the extension of chronic gastritis from the antrum into the corpus over time. This impaired barrier function may contribute to perpetuation of chronic inflammation and may be involved in H. pylori-associated carcinogenesis. Vitamin C as well as vitamin E supplements lead to some short-term protective effects on H. pylori-induced stritis but these effects seem to subside over time when the infection persists.
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