Role of oxidative stress in the pathogenesis of septic ileus in mice B. Y. DE WINTER,* L. VAN NASSAUW,  J. G. DE MAN,* F. DE JONGE,  A. J. BREDENOORD,* T. C. SEERDEN,* A. G. HERMAN, à J.-P. TIMMERMANS & P. A. PELCKMANS* *Division of Gastroenterology, Faculty of Medicine, University of Antwerp (UA), Antwerp, Belgium  Laboratory of Cell Biology and Histology, Department of Biomedical Sciences, University of Antwerp (UA), Antwerp, Belgium àDivision of Pharmacology, Faculty of Medicine, University of Antwerp (UA), Antwerp, Belgium Abstract We investigated the role of oxidative stress in the pathogenesis of septic ileus. Sepsis was induced by intraperitoneal (i.p.) injection of lipopolysaccha- rides (LPS, 20 mg kg )1 ) in mice. The effect of two i.p. injections of superoxide dismutase [polyethylene gly- col (PEG)-SOD, 4000 U kg )1 ] and catalase (PEG-CAT, 15 000 U kg )1 ) was investigated on gastric emptying, intestinal transit and total nitrite plasma concentra- tions. We also performed immunohistochemical experiments on gastric and ileal tissue. LPS signifi- cantly delayed gastric emptying and intestinal transit while plasma nitrite levels increased. Polyethylene glycol (PEG)-SOD reversed the endotoxin-induced delay in gastric emptying and improved the delay in intestinal transit without effect on plasma nitrite levels. PEG-CAT slightly improved the delay in gastric emptying without effect on intestinal transit. Immu- nohistochemistry showed the presence of nitrotyrosine (NT) and 4-hydroxy-2-nonenal (HNE) in the gastric and ileal mucosa of LPS-treated mice. Treatment with PEG-SOD or PEG-CAT of LPS mice diminished the presence of NT or HNE in both tissues. In addition, LPS induced a significant increase in inducible nitric oxide synthase (iNOS)-positive residential macroph- ages in the external musculature of stomach and ileum, which significantly decreased after PEG-SOD or PEG-CAT treatment. The present results support a role for oxidative and nitrosative stress in the patho- genesis of septic ileus in mice. Keywords catalase, endotoxin, ileus, oxidative stress, sepsis, superoxide dismutase. INTRODUCTION Oxidative stress occurs when the production of react- ive oxygen species (ROS) overwhelms the antioxidant defence mechanisms. Oxidative stress is involved in a wide range of human pathologies, including ischaemia/ reperfusion, inflammation, neurodegenerative diseases and sepsis. 1–6 ROS are potentially toxic by-products of reduced oxygen, such as superoxide anion (O  2 ), hydroxyl radical (OH • ) and non-radical oxidants, such as hydrogen peroxide (H 2 O 2 ), hypochlorous acid (HOCl) and hydroperoxides (ROOH). 2–4,6–8 NO • is another free radical (further described as nitric oxide, NO) that is poorly reactive with most biomolecules but highly reactive with other free radicals. NO reacts with molecular oxygen, O  2 and transition metal cations, leading to the formation of reactive nitrogen species (RNS). The literature on the free radical reactions of NO has largely focussed on its fast reaction with O  2 resulting in the formation of peroxynitrite (ONOO ) ), which is more reactive and cytotoxic than its precur- sors. 4,6,9,10 RNS and ROS can react with and damage many important biological molecules, including lipids, proteins and nucleic acids generating new radi- cals. 2,4,6,8,11 Under normal circumstances antioxidant defence mechanisms protect cells against ROS. Super- oxide dismutase (SOD) converts O  2 to H 2 O 2 and oxygen. Catalase (CAT) and glutathione peroxidase are capable of removing H 2 O 2 . 4,6,8 The purpose of our study was to investigate the role of oxidative and nitrosative stress in gastrointestinal (GI) complications associated with sepsis in mice. Address for correspondence B. Y. De Winter, Division of Gastroenterology, Faculty of Medicine, University of Antwerp (campus Drie Eiken), Universiteitsplein 1, 2610 Antwerp, Belgium. Tel: 32-3-820-27-10; fax: 32-3-820-25-67; e-mail: benedicte.dewinter@ua.ac.be Received: 29 July 2004 Accepted for publication: 7 October 2004 Neurogastroenterol Motil (2005) 17, 251–261 doi: 10.1111/j.1365-2982.2004.00618.x Ó 2004 Blackwell Publishing Ltd 251