Anti-inflammatory Effects of Onion Bulb Extract in the Murine DSS-Colitis Model

Abstract

The research is conducted as a contribution to existing literature to determine if onion bulb extract (OBE) reduces colitis severity in mice using treatment, prophylactic, and preventative approaches and the mechanism(s) responsible for these effects. Colitis was induced in mice by dextran sulfate sodium (DSS) daily administration in drinking water. For the treatment approach, mice received DSS for 4 days followed by daily i.p. injections of OBE/vehicle administration for 3 days (without DSS administration). For the prophylactic approach, mice received daily i.p. injections of OBE/vehicle along with DSS administration for 5 days. For the preventative approach, mice initially received daily i.p. injections of OBE/vehicle for 7 days, followed by DSS administration for 5 days (without OBE/vehicle treatment). Colitis severity was determined at the gross and histological levels. The colonic level/activity of various cytokines and chemokines were measured using proteome profiling-based assays, western blotting, and immunofluorescence techniques. In vitro neutrophil superoxide release and survival were assessed by chemiluminescence and Annexin-V/7AAD assays, respectively. DSS-induced colitis was significantly reduced by OBE treatment using all three approaches at both gross and histological levels. OBE was also shown to reduce the colonic expression and activity of several pro-inflammatory molecules and signaling pathways, various cytokines and chemokines, and molecules involved in the apoptotic machinery. In addition, OBE inhibited superoxide release and increased the spontaneous apoptosis of neutrophils. OBE showed anti-inflammatory actions, attributed in part to the modulation of the expression and activity of important pro-inflammatory molecules and signaling pathways involved in the inflammatory response.