title: Cytokine modulation of Na(+)-dependent glutamine transport across the brush border membrane of monolayers of human intestinal Caco-2 cells.
abstract: Previous studies have demonstrated that Na(+)-dependent brush border glutamine transport is diminished in septic patients. To examine the potential regulation of this decreased transport by endotoxin, cytokines, or glucocorticoids, the human intestinal Caco-2 cell line was studied in vitro. Na(+)-dependent glutamine transport across the apical brush border membrane was assayed in confluent monolayers of differentiated cells that were 10 days old. Uptake of 50 microM glutamine was determined after a 12-hour incubation with varying doses (10 to 1000 U/mL) of tumor necrosis factor-alpha, interleukin-1, interleukin-6, interferon-gamma, and various combinations of these cytokines. Studies were also done in cells incubated with E. coli endotoxin (1 micrograms/mL) or dexamethasone (1 and 10 microM). Endotoxin, tumor necrosis factor, interleukin-1, and interleukin-6 alone and in combination did not significantly reduce Na(+)-dependent glutamine transport across the brush border of Caco-2 cells. Dexamethasone decreased glutamine transport by 20%, but this decrease was not apparent for 48 hours. Interferon consistently decreased glutamine transport by 30%; this was due to a reduction in carrier maximal transport velocity (3427 +/- 783 pmol/mg protein/minute in controls versus 2279 +/- 411 in interferon, p less than 0.05) rather than a change in Km (276 +/- 29 microM in controls versus 333 +/- 74 in interferon, p = not interferon + dexamethasone + tumor necrosis factor + interleukin-1 resulted in a 38% decrease in transport activity. Cytokines and glucocorticoids may work independently and synergistically in regulating Na(+)-dependent brush border glutamine transport in human intestinal cells. Whether these signal molecules play a central role in the cause of the diminished brush border glutamine transport that occurs in septic patients requires further study.
authors.affiliation: Department of Surgery, University of Florida College of Medicine, Gainesville.
authors.forename: W W
authors.initials: WW
authors.lastname: Souba
authors.forename: E M
authors.initials: EM
authors.lastname: Copeland
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology; D001693:Biological Transport, Active / Q000502:physiology; D003110:Colonic Neoplasms / Q000473:pathology; D016207:Cytokines / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D004731:Endotoxins / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008871:Microvilli / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism*
chemical_list: D016207:Cytokines; D004731:Endotoxins; D005973:Glutamine; D003907:Dexamethasone; D012964:Sodium