Tumor necrosis factor-alpha induces Cl- and K+ secretion in human distal colon driven by prostaglandin E(2)

Increased levels of tumor necrosis factor-alpha (TNF-alpha) have been found in, for example, inflammatory bowel disease (IBD) and human immunodeficiency virus (HIV) infection. To investigate a possible contribution of TNF-alpha to the pathogenesis of diarrhea in these diseases, ion transport of human distal colon was studied in the Ussing chamber in vitro. Serosal addition of TNF-alpha increased short-circuit current (I-sc) of partially stripped tissues in a dose-dependent manner. Maximum I-sc increase of 1.8 +/- 0.2 mu mol . h(-1). cm(-2) was reached after 60 +/- 9 min at 200 ng/ml TNF-alpha. Bidirectional tracer flux measurements revealed that TNF-alpha induced an increase in Cl-36(-) serosal-to-mucosal flux, a decrease in Cl-36(-) mucosal-to-serosal flux, and a slight increase in K+ secretion indicated by an increased secretory Rb-86 net flux. In the highly differentiated colonic epithelial cell line HT-29/B6, TNF-alpha had no effect on I-sc, suggesting a mediation step located in the subepithelium. This supposition was supported by measurements on totally stripped human tissues, since removal of subepithelial layers by total stripping reduced the TNF-alpha effect by 40%. Experiments with tetrodotoxin (10(-6) M) indicated that the TNF-alpha effect was not mediated by the enteric nervous system. The specific 5-lipoxygenase blocker ICI-230487 (5 x 10(-8) M) also had no effect on TNF-alpha action. In contrast, inhibition of cyclooxygenase by indomethacin (10(-6) M) inhibited the effect of TNF-alpha. Radioimmunoassay of prostaglandin E(2) (PGE(2)) in the serosal bathing solution revealed an increase in PGE(2) production/release after addition of TNF-alpha, which paralleled the I-sc response. We conclude that TNF-alpha changed Cl- and K+ transport toward secretion in human colon. This effect was mediated by PGE(2) produced by subepithelial cells. Thus TNF-alpha could be a mediator of diarrhea during intestinal inflammation, e.g., in IBD and HIV infection.