Anti-inflammatory activity of different varieties of raisins (Vitis viniferaL.) in human gastric epithelial cells: a comparative study

Gastritis is an inflammatory disease involving millions of people in the world and Helicobacter pylori (H. pylori) is the main aetiological agent. During H. pylori infection, macrophages release several cytokines, such as TNFα, which in turn lead to the activation of transcription factor NF-κB in epithelial gastric cells. NF-κB plays a key role in IL-8 regulation, the chemokine mostly released by gastric epithelial cells during gastric inflammation. Raisins are dried grapes largely consumed in the Mediterranean area; they are an important dietary source of potassium, fibers and polyphenols. In literature, different studies have documented the potential health benefits of these fruits; methanol extracts from raisins already showed anti-inflammatory properties in human gastric epithelial cells (AGS); however, no studies regarding the anti-inflammatory activity of the water extract, that is the mostly used for food supplements preparation, have been reported until now. The aim of this study was to compare the anti-inflammatory activity of the water and hydroalcoholic extracts from different varieties of raisins (Vitis vinifera L.) at gastric level. The extracts were prepared from five different varieties of raisins and screened for their ability to inhibit IL-8 secretion in AGS cells stimulated with TNFα (10 ng/mL). Active extracts were further investigated on the NF-κB nuclear translocation by ELISA assay. IL-8 promoter activity was assayed transfecting cells with a reporter plasmid containing luciferase gene under control of human IL-8 gene promoter. Among raisin extracts, only one variety (2) significantly inhibited IL-8 secretion at 100 μg/mL; in particular, the hydroalcoholic extract showed higher reduction of IL-8 release with respect to the water extract (IC50: 26.12 and 94.18 μg/mL, respectively). Macroscopical evaluation of sample 2 fruits showed the presence of seeds, whereas the other varieties were seedless. In order to investigate the contribution of seeds, hydroalcoholic extracts from fruits and seeds were prepared and individually tested on IL-8 release, IL-8 promoter activity and NF-κB nuclear translocation; seeds extract inhibited all the previous parameters in concentration-dependent manner, showing higher efficacy with respect to fruit. These results suggest that seeds could have an important contribution in the anti-inflammatory activity of raisins and their consumption could confer a beneficial effect to the gastric inflammatory diseases.