A novel in vitro infection model of Helicobacter pylori using mucin-producing murine gastric surface mucous cells

Mucin immobilization in calcium alginate: A possible mucus mimetic tool for evaluating mucoadhesion and retention of flavour

To reduce animal testing, there is a need to develop novel in-vitro models for evaluating the retention of bioactive compounds in food and pharmaceutical products. Here, a mucus-mimetic platform was developed through a one-step approach based on encapsulating mucin within alginate gel beads. We found that mucins form micron sized aggregates distributed across the surface of the calcium-alginate bead, as shown by environmental scanning electron microscopy (ESEM). Retention of bioactive compounds on the mucin-functionalised surface was tested using a commercial orange drink formulation. To aid flavour retention, different mucoadhesive polymers with varying charge, including anionic, neutral and strongly cationic, were tested for their ability to interact with mucin and aid retaining flavour compounds within the mucin-alginate bead. The alginate-mucin mucus mimic was validated using an ex-vivo bovine tongue, with the flavour retention results showing qualitative agreement. The developed method proved to be a convenient, efficient tool for providing information on the effectiveness of mucoadhesive polymers without variability, safety and sustainability issues associated with an ex-vivo or in-vivo system. We propose that by encapsulating other relevant oral proteins, alongside mucins, current gaps between in-vitro and the ex-vivo systems may be narrowed.

Studies of Lewis antigens and H. pylori adhesion in CHO cell lines engineered to express Lewis b determinants

Many microbes bind and adhere via adhesins to host cell carbohydrates as an initial step for infection. Therefore, cell lines expressing Lewis b (Le(b)) determinants were generated as a potential model system for Helicobacter pylori colonization and infection, and their expression of blood group Lewis determinants was characterized. CHO-K1 cells were stably transfected with selected glycosyltransferase cDNAs, and two Le(b) positive clones, 1C5 and 2C2, were identified. Expression of Lewis (Le(a), Le(b), Le(x), and Le(y)) determinants was analyzed by flow cytometry of intact cells, SDS-PAGE/Western blot of solubilized glycoproteins, and thin layer chromatography immunostaining of isolated glycolipids (GL). Binding of H. pylori to cells was examined by microscopy and quantified. Flow cytometry showed that 1C5 and 2C2 were Le(a) and Le(b) positive. 1C5 expressed Le(b) on O-linked, but not N-linked, glycans and only weakly on GLs. In contrast, 2C2 expressed Le(b) on N-, O-glycans, and GLs. Furthermore, both clones expressed Le(a) on N- and O-glycans but not on GLs. 2C2, but not 1C5, stained positively for Le(y) on N-linked glycans and GLs. Both clones, as well as the parental CHO-K1 cells, expressed Le(x) on GLs. A Le(b)-binding H. pylori strain bound to the 1C5 and 2C2 cells. In summary, two glycosyltransferase transfected CHO-K1 cell clones differed regarding Lewis antigen expression on N- and O-linked glycans as well as on GLs. Both clones examined supported adhesion of a Le(b)-binding H. pylori strain and may thus be a useful in vitro model system for H. pylori colonization/infection studies.

A novel approach for screening of new anti-Helicobacter pylori substances

Gastric mucosal cell-derived L-lactic acid strongly enhances proliferation of Helicobacter pylori, and may contribute to the long-term colonization of H. pylori in the stomach. Therefore it is assumed that inhibitory substances active against L-lactic acid-dependent growth of H. pylori will be useful candidates as novel therapeutic agents for H. pylori infection. In this study, we developed a new assay system for screening anti-H. pylori substances, and baicalein and glycyrrhetinic acid were found as potent inhibitory substances against L-lactic acid-dependent H. pylori growth but not L-lactic acid-independent growth. The newly developed assay system described in this study also may facilitate the development of novel therapeutic agents for H. pylori infection.

NF-kappaB activation during acute Helicobacter pylori infection in mice

Nuclear factor kappaB (NF-kappaB) plays a key regulatory role in host cell responses to Helicobacter pylori infection in humans. Although mice are routinely used as a model to study H. pylori pathogenesis, the role of NF-kappaB in murine cell responses to helicobacters has not been studied in detail. We thus investigated the abilities of different Helicobacter isolates to induce NF-kappaB-dependent responses in murine gastric epithelial cells (GECs) and in transgenic mice harboring an NF-kappaB-responsive lacZ reporter gene. H. pylori and Helicobacter felis strains up-regulated the synthesis in mouse GECs of the NF-kappaB-dependent chemokines KC (CXCL1) and MIP-2 (CXCL2). These responses were cag pathogenicity island (cagPAI) independent and could be abolished by pretreatment with a pharmacological inhibitor of NF-kappaB. Consistent with the in vitro data, experimental Helicobacter infection of transgenic mice resulted in increased numbers of GECs with nuclear beta-galactosidase activity, which is indicative of specific NF-kappaB activation. The numbers of beta-galactosidase-positive cells in mice were significantly increased at day 1 postinoculation with wild-type H. pylori strains harboring or not harboring a functional cagPAI, compared to naive animals (P = 0.007 and P = 0.04, respectively). Strikingly, however, no differences were observed in the levels of gastric NF-kappaB activation at day 1 postinoculation with H. felis or at day 30 or 135 postinoculation with H. pylori. This work demonstrates for the first time the induction of NF-kappaB activation within gastric mucosal cells during acute H. pylori infection. Furthermore, the data suggest that helicobacters may be able to regulate NF-kappaB signaling during chronic infection.

L-lactic acid secreted from gastric mucosal cells enhances growth of Helicobacter pylori

BACKGROUND

Helicobacter pylori mainly inhabit the mucus layer in the gastric mucosa. However, mechanisms involving H. pylori colonization and proliferation in gastric mucosa are not well established. This study focuses on elucidating the role of gastric mucosal cells on growth of H. pylori.

MATERIALS AND METHODS

H. pylori was co-cultured with the murine gastric surface mucosal cells (GSM06), and the growth of H. pylori on the cells was assessed by enumerating the colony-forming units (CFU). The H. pylori growth factor in the culture media conditioned by GSM06 cell was purified by HPLC, and the chemical structure of the growth factor was identified by analyses of (1)H- and (13)C-NMR spectra.

RESULTS

A marked increase in the number of CFU of H. pylori was observed in the GSM06 cells. The enhanced H. pylori growth was also observed when indirectly incubated with GSM06 cells through semi-permeable membrane. In addition, culture media conditioned by GSM06 cell stimulated H. pylori growth approximately one thousand-fold. By bioassay-guided purification, the H. pylori growth factor was isolated from the conditioned medium of GSM06 cells and identified as L-lactic acid. The H. pylori growth-enhancing activity under microaerobic condition was well correlated with L-lactic acid concentrations in the conditioned media.

CONCLUSIONS

This study demonstrates that L-lactic acid secreted by gastric mucosal cells enhances the growth of H. pylori, and this L-lactic acid-dependent growth of H. pylori may be important to the long-term colonization of H. pylori in the stomach.

The immortalized cell lines with differentiation potentials: their establishment and possible application

Approximately 200 types of the cells are qualified as differentiated cells in the human body. If these different types of cells can be separated from each other (or cloned) and obtained in sufficient quantity, it will be beneficial for studying development, morphogenesis, tissue maintenance, cancer and aging, and for reconstructing functional tissues in vitro for regenerative medicine. We produced the transgenic mouse and rat harboring SV40 T-antigen gene to make the immortalized cell lines in the primary tissue culture and succeeded in establishing many functionally active cell lines from various tissues. Many immortalized cell lines from various tissues are shown to exhibit the unique characteristics of tissue functions and they should be useful as an in vitro model of various tissues for physiological and pharmacological investigations. Future application of these cells to drug screening is discussed.