Strawberry tannins (Fragaria X ananassa Duch.): evaluation of the in vitro anti-inflammatory activity at gastric level

Gastritis is an inflammation of gastric mucosa caused for 90% of cases by the presence of the bacterium Helicobacter pylori (H. pylori). During H. pylori infection macrophages produce pro-inflammatory cytokines, including TNFα, leading to the NF-κB activation in gastric epithelial cells. NF-κB activation increases the transcription of several inflammatory genes, including IL-8. Strawberry is one of the most commonly consumed fruits in the world; it contains high amount of polyphenols, including anthocyanosides and tannins. Gastric effects of strawberry have been documented by some in vitro and in vivo studies; however, these effects have been associated to the presence of anthocyanosides, while the contribution of tannins from strawberry against gastric inflammation has not been fully investigated. In particular, no data have shown the capacity of tannins-enriched extract from strawberry to inhibit IL-8 secretion and NF-κB pathway in epithelial gastric cells, before and after in vitro gastric digestion. The aim of this work was to evaluate the effect of tannins from strawberry (Fragaria X Ananassa Duch.) in an in vitro model of gastric inflammation. Agrimoniin and casuarictin were isolated from strawberry extract and assayed in human gastric epithelial cells (AGS) stimulated with TNFα (10 ng/mL). NF-κB driven transcription and IL-8 promoter activity were evaluated by transient transfection assays in AGS cells with report plasmids, while NF-κB nuclear translocation and IL-8 secretion were performed by an ELISA assay. Agrimoniin and casuarictin, which belong to the class of ellagitannins, were the most abundant molecules of the extract, while procyanidin B1 was analyzed in order to evaluate the contribution of condensed tannins to the anti-inflammatory activity. After in vitro gastric digestion, agrimoniin and casuarictin decreased (-26.4% and -5.7% respectively), while procyanidin B1 showed a strongly increase (+34.9%) probably due to the degradation of condensed tannins. All the three molecules were able to inhibit IL-8 secretion showing different mechanisms: casuarictin seems to affect exclusively NF-κB pathway, procyanidin B1 seems to act in NF-κB independent way while agrimoniin seems to be able to influence NF-κB and other pathways. These results suggest that tannins from strawberry could exert a beneficial effect on gastric inflammation; agrimoniin, casuarictin and procyanidin B1 explain, at least in part, the biological effects observed with the extract.