AIM: To study isolation and chemical characterization of pectin derived from the common cranberry Vaccinium oxycoccos L. (oxycoccusan OP) and the testing of its preventive effect on experimental colitis.METHODS: Mice were administrated orally with OP two days prior to a rectal injection of 5% acetic acid and examined for colonic damage 24 h later. Colonic inflammation was characterized by macroscopical injury and enhanced levels of myeloperoxidase activity measured spectrophotometrically with o-phenylene diamine as the substrate. The mucus contents of the colon were determined by the Alcian blue dye binding method. Vascular permeability was estimated using 4%Evans blue passage after i.p. injection of 0.05 mol/L acetic acid.RESULTS: In the mice treated with OP, colonic macroscopic scores (1.1 ± 0.4 vs 2.7, P ＜ 0.01) and the total square area of damage (10 ± 2 vs 21 ± 7, P ＜ 0.01)were significantly reduced when compared with the vehicle-treated colitis group. OP was shown to decrease the tissue myeloperoxidase activity in colons (42 ± 11 vs 112 ± 40, P ＜ 0.01) and enhance the amount of mucus of colitis mice (0.9 ± 0.1 vs 0.4 ± 0.1, P ＜ 0.01). The level of colonic malondialdehyde was noted to decrease in OP-pretreated mice (3.6 ± 0.7 vs 5.1 ± 0.8, P ＜ 0.01).OP was found to decrease the inflammatory status of mice as was determined by reduction of vascular permeability (161 ± 34 vs 241 ± 21, P ＜ 0.01). Adhesion of peritoneal neutrophils and macrophages was also shown to decrease after administration of OP (141 ± 50vs 235 ± 37, P ＜ 0.05).CONCLUSION: Thus, a preventive effect of pectin from the common cranberry, namely oxycoccusan OP,on acetic acid-induced colitis in mice was detected.A reduction of neutrophil infiltration and antioxidant action may be implicated in the protective effect of oxycoccusan.