Evaluation of the anti-inflammatory activity of raisins (Vitis vinifera L.) in human gastric epithelial cells: a comparative study

Gastritis is an inflammatory disease involving millions of people in the world; about 90% of cases of gastritis are caused by the presence of the bacterium Helicobacter pylori (H. pylori) while only 10% is due to other risk factors including autoimmune reactions, drugs, and alcohol. During H. pylori infection, macrophages release several cytokines, such as TNFα, which in turn lead to the activation of the transcription factor NF-κB in epithelial gastric cells (Mai et al., 1991). NF-κB is strictly involved in the expression of a variety of inflammatory genes, including IL-8 (Yasumoto et al., 1992). This chemokine is mostly released by gastric epithelial cells during gastric inflammation (Shimada et al., 1998). 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), these extracts were able to decrease protein and mRNA levels of ICAM-1 in TNFα stimulated cells (Kaliora et al., 2008). However, no studies regarding the anti-inflammatory activity of the hydro-alcoholic or water extracts, 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 hydro-alcoholic extracts of raisins from different origins (var. sultana, Vitis vinifera L.) at gastric level. The extracts were prepared from five different raisins: one from Portugal (sample 1), one from Turkey (sample 2) and three commercially available (sample 3,4 and 5); the extracts were screened for their ability to inhibit IL-8 release in AGS cells stimulated with TNFα (10 ng/mL); IL-8 secretion and NF-κB nuclear translocation were assayed by ELISA assays. NF-κB driven transcription and IL-8 promoter activity were assayed transfecting cells with reporter plasmids containing luciferase gene, in particular: NF-κB-Luc plasmid containing E-selectin promoter characterized by the presence of three responsive elements κB and IL-8-Luc plasmid containing human IL-8 gene characterized by the presence of a binding site for NF-κB. Among raisin extracts, only sample 2 significantly inhibited IL-8 secretion at 100 μg/mL; in particular, the hydro-alcoholic extract showed higher reduction of TNFα –induced IL-8 release with respect to the water extract (IC50: 3.34 vs. 94.18 μg/mL, respectively). Macroscopic evaluation of sample 2 raisin showed the presence of seeds, whereas the other raisins samples were seedless. In order to investigate the contribution of seeds, the hydro-alcoholic extracts from fruit and seeds were prepared and individually tested on IL-8 release, IL-8 promoter activity, NF-κB driven transcription and nuclear translocation; seeds extract inhibited all the previous parameters in a concentration-dependent manner, showing higher efficacy than fruit extract. IC50 from the seeds extract was lower than the fruit extract in each parameter evaluated. 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 against gastric inflammatory diseases. Mai et al. (1991). J Clin Invest. 87, 894-900 Yasumoto et al. (1992). The Journal of biological chemistry. 267, 22506-22511 Shimada et al. (1998). Journal of gastroenterology. 33, 613-617 Kaliora et al. (2008). Nutr Cancer. 60(6):792-9