MPO and colitis: In hapten (2,4-dinitrobenzene sulfonic acid)-induced colitis in Sprague–Dawley rats, subcutaneous nicotine (a single dose of 8 mg/kg or triple doses of 4 mg/kg nicotine) reduced the colonic lesion size, MPO activity, luminol-amplified free radical generation, and leukotriene B4 (LTB4) formation by downregulating the colonic IL-1β and monocyte chemoattractant protein (MCP)-1 protein expression in the inflamed colon of animals with colitis (25).