Redox imaging of dextran sodium sulfate-induced colitis mice treated with nitric oxide synthase inhibitors

Abstract

Ulcerative colitis (UC) is an inflammatory bowel disease of unknown cause. Redox imbalance, as characterized by excessive production of reactive oxygen species (ROS) and nitric oxide (NO), and deficient levels of endogenous antioxidants, is associated with the pathogenesis of UC. Overhauser-enhanced magnetic resonance imaging (OMRI) combined with a spin-probe method produces high-resolution images of redox imbalance in disease states. We aimed to investigate the effect of NO synthase (NOS) inhibitors on colonic ROS generation in mice with colitis induced by dextran sodium sulfate (DSS) using the OMRI/spin-probe method. Symptoms of DSS-induced colitis were ameliorated by an inducible NOS (iNOS) inhibitor, aminoguanidine (AG), but not by a non-selective NOS inhibitor, NG-Nitro-L-arginine methyl ester (L-NAME). Intracellular ROS generation, observed as the enhancement of OMRI contrast decay rates of a 3-methoxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl probe in the colons of DSS-induced colitis mice, was suppressed by AG, in agreement with the results of an in vivo electron spin resonance study. AG had an inhibitory effect on ROS production at the upper colon and rectum during the initiation stage of colitis, and at the upper and lower colon during the advanced stage. Additionally, there were partial differences in the localization of iNOS protein and nitrite/nitrate levels. L-NAME treatment showed a tendency for increased ROS generation at the upper colon during the advanced stage. The OMRI/spin-probe method provides a novel tool for screening ROS inhibitory activity in vivo in DSS-induced colitis mice.