Location of superoxide anion generation in human colonic mucosa obtained by biopsy.

To identify which cells generate superoxide, inflamed human mucosa was tested with nitro-blue tetrazolium as a probe, because it is reduced by strong reducing agents to form insoluble blue formazan, which then precipitates in tissues. Biopsy specimens from control subjects and patients with ulcerative colitis were studied. The specimens were organ cultured with bubbling air or nitrogen, and inhibition of the reduction by catalase (a hydrogen peroxide scavenger), para-benzoquinone (a tissue permeable superoxide scavenger), or superoxide dismutase (a superoxide scavenger) was assayed. The dye was reduced by epithelial cells, vascular endothelium, and infiltrating mononuclear cells of the mucosa. Its reduction by vascular endothelium and infiltrating mononuclear cells was greater in inflamed mucosa. The reduction by vascular endothelium and infiltrating mononuclear cells was inhibited in cultures with nitrogen saturation or with 1 mM para-benzoquinone. The vascular endothelium seems to produce superoxide in the inflamed mucosa, which would exacerbate tissue injury in ulcerative colitis.