Glutamine Modulates LPS-Induced IL-8 Production through IκB/NF-κB in Human Fetal and Adult Intestinal Epithelium

Abstract

The intestinal epithelium may serve as a nidus for inflammation that can cause local and systemic organ dysfunction. Relative to the adult, the immature intestine is exquisitely sensitive to inflammatory agents. Glutamine (Gln), an amino acid that is rapidly depleted during critical illness, modulates intestinal inflammation in vitro and in vivo. Here we relate Gln status to activation of the inhibitor of κB (IκB)/nuclear factor (NF)-κB signaling pathway in fetal-derived (H4) and adult (Caco-2) enterocytes. In the absence of Gln with or without LPS, H4 cells expressed more interleukin (IL)-8) than Caco-2 cells. Gln supplementation partially prevented the LPS-induced elevation of IL-8 in both cell types. IκBα was significantly decreased in both H4 and Caco-2 cells with Gln deprivation, and this was followed by an increase in NF-κB p65 in the nucleus. DNA binding of NF-κB was increased in both H4 and Caco-2 cells with Gln deprivation. IκBα phosphorylation was not altered by Gln status in either H4 or Caco-2 cells. Proteasomal inhibition after Gln depletion in Caco-2 cells was associated with an increase in the IκB-ubiquitin complex, but a decrease in complex formation in H4 cells, indicating that Gln deprivation alters IκBα through a pathway that differs from Caco-2 cells. We speculate that a reduced capacity of the immature enterocyte (H4) to respond to Gln deprivation with increased synthesis of IκBα rather than increased proteolysis as seen in the Caco-2 cells is the underlying mechanism.