Pomegranate Mesocarp against Colitis-Induced Visceral Pain in Rats: Effects of a Decoction and Its Fractions

Abstract

The management of chronic visceral pain related to Inflammatory Bowel Diseases or Irritable Bowel Syndrome is still a clinical problem and new therapeutic strategies continue to be investigated. In the present study, the efficacy of a pomegranate decoction and of its polysaccharide and ellagitannin components in preventing the development of colitis-induced abdominal pain in rats was evaluated. After colitis induction by 2,4-dinitrobenzenesulfonic acid (DNBS), the pomegranate decoction (300 mg kg^-1), polysaccharides (300 mg kg^-1), and ellagitannins (45 mg kg^-1) were orally administered for 14 days. Repeated treatment with decoction reduced visceral hypersensitivity in the colitic animals both at 7 and 14 days. Similar efficacy was shown by polysaccharides, but with lower potency. Ellagitannins administered at dose equivalent to decoction content showed higher efficacy in reducing the development of visceral pain. Macroscopic and microscopic evaluations performed on the colon 14 days after the damage showed that all three preparations reduced the overall amount of mast cells, the number of degranulated mast cells, and the density of collagen fibers in the mucosal stroma. Although ellagitannins seem to be responsible for most of the beneficial effects of pomegranate on DNBS-induced colitis, the polysaccharides support and enhance its effect. Therefore, pomegranate mesocarp preparations could represent a complementary approach to conventional therapies for promoting abdominal pain relief.

Keywords: DNBS; IBDs; IBS; chronic visceral pain; colitis; ellagitannins; polysaccharides; punicalagin; rats.

Figure 1

Composition of the dry decoction in terms of phenolic constituents and crude polysaccharides. Distribution of the phenolic compounds, total phenolic content, and crude polysaccharide amount. The data are expressed as a mean of a triplicate, as mg/g dry decoction.

Figure 2

Effect of repeated treatment with pomegranate-based preparations on visceral hypersensitivity. Tests were performed before the treatments (a), 7 (b) and 14 (c) days after the damage induction, measuring the Visceromotor Response (VMR) to the Colorectal Balloon Distension (CRD). Each value is the mean ± S.E.M. and represents the mean of six rats per group. * p < 0.05 and ** p < 0.01 vs. vehicle + vehicle treated animals. ^ p < 0.05 and ^^ p < 0.01 vs. 2,4-dinitrobenzenesulfonic acid (DNBS) + vehicle treated animals.

Figure 3

Effect of repeated treatment with pomegranate-based preparations on behavioral alterations related to pain perception. Behavioral responses to CRD were assessed Abdominal Withdrawal Reflex (AWR) measurement, using a semiquantitative score in conscious animals. Tests were performed 14 days after DNBS administration in awake animals. Each value is the mean ± S.E.M. and represents the mean of six rats per group. ** p < 0.01 vs. vehicle + vehicle treated animals ^^ p < 0.01 vs. DNBS + vehicle treated animals.

Figure 4

Effect of repeated treatment with pomegranate-based preparations on colon macroscopic damage. Animals were sacrificed 14 days after DNBS injection, and the colon portion was removed to perform the macroscopic analysis. The Macroscopic Damage Score (MDS) was used to quantify the tissue damage degree. Each value is the mean ± S.E.M. and represents the mean of six rats per group. ** p < 0.01 vs. vehicle + vehicle treated animals. ^^ p < 0.01 vs. DNBS + vehicle treated animals.

Figure 5

Effect of repeated treatment with pomegranate-based preparations on colon microscopic damage. Microscopic evaluations were carried out 14 days after DNBS injection by light microscopy on sections of colon. Histological evaluations were performed on sections stained with hematoxylin and eosin (a, scale bar: 20×), picrosirius red staining (b, scale bar: 40×), and tryptase immunohistochemistry (d, scale bar: 40×, insert: 100×). For picrosirius red analysis, a morphometric quantitative evaluation of the staining intensity (expressed as volume density) was performed on the digital images (c). The reported values are the means ± SEM of the measurements of individual animals (at least five images each) from the different experimental groups. ** p ˂ 0.01 vs. vehicle + vehicle group. ^^ p ˂ 0.01 vs. DNBS + vehicle group.