The effect of oleuropein on chronic intestinal inflammation in C57BL/6 mice

E Giner-Ventura, MC Recio, JL Ríos, RM Giner-Pons. University of Valencia, Pharmacology 46100, Spain

Introduction. Ulcerative colitis and Crohn’s disease, considered to be the major inflammatory bowel diseases (IBD), are characterized by episodes of acute inflammation followed by periods of disease remission. Over time, the chronic inflammation of the colon increases the risk of developing colorectal cancer. In previous studies, we have demonstrated the protective effect of oleuropein, the predominant secoiridoid in leaves and fruits of the olive tree (Olea europaea L.), in an acute dextran sulphate sodium (DSS)-induced model of colitis in mice. The compound prevents cytokine formation, NO generation, iNOS, and MMP-9 and COX-2 expression through the inhibition of NF-κB p65 translocation to the nucleus (Giner et al., 2011). In the present study, our objective is to examine the beneficial effects of this compound on a chronic murine model of DSS-induced colitis.

Experimental approach. Female C57BL/6 mice were randomized (7-10 animals in each group) to receive four cycles of DSS (1% DSS during the first and the second cycle followed by 2% DSS during the third and fourth cycle). Each cycle consisted of 7 days of DSS in drinking water followed by 7 days of water without DSS. The mice were fed a control diet or a diet supplemented with 0.25% oleuropein throughout the experiment. The animals were sacrificed by cervical dislocation on day 56 and their colons were removed and submitted for macroscopic examinations. The disease activity index score (DAI) was analyzed taking weight loss, stool blood, and rectal bleeding into consideration. Several pro-inflammatory mediators were measured with the aid of biochemical assays, PCR and Western blot analysis. Statistical significance was determined by analysis of variance (ANOVA) and Dunnet’t test.

Key results and discussion. Oleuropein was found to significantly reduce the colonic weight/length ratio (an index of colonic oedema associated with the inflammatory response) by 20% (p<0.05) with respect to the DSS group. The extent and severity of injury to the colon, as indicated by the DAI score, was ameliorated by the secoiridoid (1.00 ± 0.13 for the DSS group vs. 0.47 ± 0.08 (p<0.01) for the oleuropein group). It also reduced the expression of the pro-inflammatory enzymes COX-2 and iNOS by 68% (p<0.01) and 58% (p<0.01), respectively, and inhibited the p38 phosphorylation by 50% (p<0.01) in the colon tissue.

In this report, we show for the first time that oleuropein is active on a chronic DSS-induced model. Several studies have shown that this compound has several antitumor effects in mice (Hamdi & Castellon, 2005); moreover, its aglycone form was shown to exert antiproliferative effects in Caco-2 cells, perhaps mediated, in part by the inhibition of phosphorylation p38 MAPK and CREB (Corona et al., 2007). Oleuropein may thus be a potential protective agent against chronic IBD.

Acknowledgement. We thank the Spanish Government, MICIIN (SAF 2009-13059-C03-01). E.Giner is the recipient of a fellowship from the VLC Campus Universitat de Valencia (V Segles).

References. Corona et al. Biochem Bio Res Commun 2007; 362:606-611. Giner et al. J Agr Food Chem. 2011; 59:12882-12892. Hamdi & Castellon. Biochem Biophys Res Commun 2005;334:769-778.