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Superoxide output and expression of NADPH oxidase 1 in human colonic epithelial cells


Translocation of microorganisms from the gut lumen may contribute to morbidity in sepsis. Conservation of normal barrier function should, therefore, be a goal in critical illness, but its components is only partly defined. Beyond mechanical contribution, the colonic epithelium may possess antimicrobial activity via yet undefined mediators [1]. Superoxide (O2-), generated by membrane-bound NADPH oxidase (Nox), is a key antimicrobial agent of phagocytes, but output from human colonic epithelial cells has not been demonstrated.


To measure O2- output and expression of the non-phagocytic NADPH oxidase, Nox1, in short term cultures of primary epithelial cells from normal human colon and in Caco-2 colonic epithelial cell line.


Colonic epithelial cells were isolated from biopsies of subjects with uninflamed bowel and Caco-2 cells were grown in 24-well plates [2]. Output of O2- was measured by the cytochrome c assay or luminol-enhanced luminescence and localised by the nitrobluetetrazolium (NBT) assay [3].Effects of 1 mM NADPH, oxidoreductase inhibition by 10 µM diphenylene iodonium (DPI) and protein kinase C-activation by 0.5 µg/ml phorbol myristate ester (PMA) were assessed. mRNA expression of Nox1 was analysed by RT-PCR.


Identical results were obtained in primary epithelial cells (see Figs) and Caco-2 cells. NBT-reduction was observed at the outer cell membrane and Nox1 mRNA was detected in all cell cultures. NADPH increased output of O2- within seconds although cell membranes are impermeable to NADPH.

figure 1

Superoxide output in cultures of primary colonic epithelial cells. O2- output (mean ± SEM, n = 5) was adjusted to mg protein. *P < 0.05 compared with basal (t-test). SOD, O2- dismutase.


These results show that cultures of human colonic epithelial cells produce extracellular O2- possibly through membrane-bound Nox1, which appears to independent of protein kinase C activation. O2- from epithelial cells may possess antimicrobial activity and contribute to colonic barrier function.


  1. Shock 1995, 4: 345.

  2. Scand J Gastroenterol 2000, 35: 772. 10.1080/003655200750023471

  3. Gastroenterology 1998, 115: 1186.

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Perner, A., Andresen, L., Pedersen, G. et al. Superoxide output and expression of NADPH oxidase 1 in human colonic epithelial cells. Crit Care 5 (Suppl 1), P069 (2001).

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  • NADPH Oxidase
  • Colonic Epithelial Cell
  • Short Term Culture
  • Iodonium
  • Outer Cell Membrane