In vitro anti-inflammatory activity of Fragaria spp. in human gastric epithelial cells

Strawberries (Fragaria spp.) are commonly consumed berries, and are the most popular choice among consumers, being eaten fresh, frozen and in different processed products. The biological activity of strawberries is correlated to the presence of several compounds, including proanthocyanidins, anthocyanins and ellagitannins. The gastrointestinal tract represents an important barrier between the human hosts and microbial populations. During gastric inflammation, epithelial cells release higher levels of cytokines including IL-1β, TNFα, and IL-8, a potent neutrophil-activating chemokine that plays a central role in gastritis (Crabtree et al., 1995). This response strictly depends on the activation of NF-kB pathway (Yasumoto et al., 1992). Strawberry has been shown to inhibit ethanol-induced gastritis in rats, and the effect was related to the presence of anthocyanins (Alvarez-Suarez et al., 2011). However, the inhibitory effect of tannin-enriched fractions (TEFs) from strawberries against gastric inflammation was not previously described. The aim of the present work was to investigate if tannins from Fragaria spp. could contribute to inhibit gastric inflammation. For this purpose, berries were harvested at maturity and the extraction of polyphenols was carried out with a mixture acetone/water (70/30 v/v), as previously reported (Gasperotti et al., 2010). TEFs and agrimoniin, the most abundant ellagitannin occurring in Fragaria spp., were assayed to investigate a) the inhibition of NF-kB nuclear translocation and driven transcription; b) the effect on IL-8 release in gastric epithelial cell line (AGS) stimulated with TNFα and IL-1ß. Both TEFs from Fragaria x ananassa and Fragaria vesca inhibited TNFα-induced NF-kB driven transcription and nuclear translocation. IC50 on TNFα-induced NF-kB nuclear translocation were 0.25 and 1.01 μg/ml, respectively. Agrimoniin inhibited TNFα-induced NF-kB driven transcription and nuclear translocation in a concentration-dependent manner. When the stimulus was IL-1β, the effect of TEFs and agrimoniin were lower with respect to TNFα. Since IL-8, whose expression is strictly dependent on NF-kB activation, is widely involved in gastric inflammation, the following experiments evaluated the effect of the extracts/individual compound on IL-8 secretion in AGS cells. Both the extracts and agrimoniin were able to inhibit IL-8 release, induced by TNFα and IL- 1β, in a concentration-dependent way. IC50 of Fragaria x ananassa and Fragaria vesca extracts on TNFα-induced IL-8 release were 0.09 and 0.29 μg/ml, respectively. The effect of the extracts on TNFα-induced IL-8 release was ten fold higher than that induced by IL-1β. Agrimoniin inhibited preferentially TNFα-induced IL-8 release as well (IC50 0.042 μM). TEFs and agrimoniin also inhibited IL-8 promoter activity induced by TNFα in a concentration-dependent manner. Our results report that Fragaria spp., which are widely consumed as nutrients, show in vitro anti- inflammatory effect at the gastric level, being agrimoniin responsible, at least in part, for the biological activity exerted by the extracts. These results suggest that tannins, in addition to anthocyanins, could contribute to the beneficial effects of Fragaria spp. at the gastric level.