Grape peel powder attenuates the inflammatory and oxidative response of experimental colitis in rats by modulating the NF-κB pathway and activity of antioxidant enzymes

Abstract Most phenolic compounds and dietary fiber reach intact to the colon. We hypothesized that grape peel powder (GPP), a rich source of these bioactive compounds, modulates inflammatory and oxidative pathways collaborating to attenuate colonic damage in experimental colitis. To determine which bioactive fraction would be responsible for this effect, the aim of this study was to evaluate the effect of dietary supplementation with whole GPP or the isolated bioactive-rich fractions from GPP (extractable polyphenols –EP, dietary fiber and fiber-bound polyphenols –NEP-F, and dietary fiber –F) in rats with experimental colitis. Colitis was induced by intrarectal injection of 2,4,6-trinitrobenzene sulfonic acid (TNBS) after 15 days of dietary supplementation. EP diet did not reverse the decrease in feed intake and indeed worsened colon shortening and increased spleen weight; however, these effects were not observed for the GPP group, which had polyphenols associated to the matrix besides the extractable ones. Colitis impaired the activity of colonic antioxidant enzymes and increased lipid peroxidation, protein oxidation, nitric oxide (NO) levels, and pro-inflammatory cytokines in serum and in the colon tissue. GPP restored the activity of antioxidant enzymes and decreased colon oxidation and NO levels. All grape peel fractions reduced IKK-β protein expression and NO levels in colon tissue but only NEP-F reduced the expression of pNF-κB and myeloperoxidase activity. Results demonstrated that GPP attenuates inflammatory and oxidative response in TNBS-induced colitis by down-regulating the NF-κB pathway and up-regulating antioxidant enzymes; NEP-F being the fraction most likely associated to these protective effects.