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APPETITE, OBESITY AND METABOLISM

Glutamine and KGF each regulate extracellular thiol/disulfide redox and enhance proliferation in Caco-2 cells

Departments of ¹Medicine and ⁴Biochemistry, ²Graduate Program in Molecular and Systems Pharmacology and ⁵Center for Clinical and Molecular Nutrition, Emory University School of Medicine, Atlanta, Georgia 30322; and ³Department of Surgery, University of Rochester Medical Center, Rochester, New York 14642

Submitted 13 November 2002 ; accepted in final form 27 August 2003

Glutamine (Gln) and keratinocyte growth factor (KGF) each stimulate intestinal epithelial cell growth, but regulatory mechanisms are not well understood. We determined whether Gln and KGF alter intra- and extracellular thiol/disulfide redox pools in Caco-2 cells cultured in oxidizing or reducing cell medium and whether such redox variations are a determinant of proliferative responses to these agents. Cells were cultured over a physiological range of oxidizing to reducing extracellular thiol/disulfide redox (E_h) conditions, obtained by varying cysteine (Cys) and cystine (CySS) concentrations in cell medium. Cell proliferation was determined by 5-bromo-2-deoxyuridine (BrdU) incorporation. Gln (10 mmol/l) or KGF (10 µg/l) did not alter BrdU incorporation at reducing E_h (-131 to -150 mV), but significantly increased incorporation at more oxidizing E_h (Gln at 0 to -109 mV; KGF at -46 to -80 mV). Cellular glutathione/glutathione disulfide (GSH/GSSG) E_h was unaffected by Gln, KGF, or variations in extracellular Cys/CySS E_h. Control cells largely maintained extracellular E_h at initial values after 24 h (-36 to -136 mV). However, extracellular E_h shifted toward a narrow physiological range with Gln and KGF treatment (Gln -56 to -88 mV and KGF -76 to -92 mV, respectively; P < 0.05 vs. control). The results indicate that thiol/disulfide redox state in the extracellular milieu is an important determinant of Caco-2 cell proliferation induced by Gln and KGF, that this control is independent of intracellular GSH redox status, and that both Gln and KGF enhance the capability of Caco-2 cells to modulate extremes of extracellular redox.

cysteine; glutathione; intestine; oxidation-reduction; keratinocyte growth factor

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