Hyperosmotic stress induces nuclear factor-κB activation and interleukin-8 production in human intestinal epithelial cells

Inflammatory bowel disease of the colon is associated with a high osmolarity of colonic contents. We hypothesized that this hyperosmolarity may contribute to colonic inflammation by stimulating the proinflammatory activity of intestinal epithelial cells (IECs). The human IEC lines HT-29 and Caco-2 were used to study the effect of hyperosmolarity on the IEC inflammatory response. Exposure of IECs to hyperosmolarity triggered expression of the proinflammatory chemokine interleukin (IL)-8 both at the secreted protein and mRNA levels. In addition, hyperosmotic stimulation induced the release of another chemokine, GRO-α. These effects were because of activation of the transcription factor, nuclear factor (NF)-κB, because hyperosmolarity stimulated both NF-κB DNA binding and NF-κB-dependent transcriptional activity. Hyperosmolarity activated both p38 and p42/44 mitogen-activated protein kinases, which effect contributed to hyperosmolarity-stimulated IL-8 production, because p38 and p42/44 inhibition prevented the hyperosmolarity-induced increase in IL-8 production. In addition, the proinflammatory effects of hyperosmolarity were, in a large part, mediated by activation of Na⁺/H⁺ exchangers, because selective blockade of Na⁺/H⁺ exchangers prevented the hyperosmolarity-induced IEC inflammatory response. In summary, hyperosmolarity stimulates IEC IL-8 production, which effect may contribute to the maintenance of inflammation in inflammatory bowel disease.