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Biochemical and Molecular Actions of Nutrients

Alanylglutamine Dipeptide and Growth Hormone Maintain PepT1-Mediated Transport in Oxidatively Stressed Caco-2 Cells^1,2

B. Alteheld^*,3, M. E. Evans^,**,3, L. H. Gu, V. Ganapathy, F. H. Leibach, D. P. Jones^,** and T. R. Ziegler^,**,4

^* Department of Nutrition Science, University of Bonn, Germany; Department of Medicine and ^** Center for Clinical and Molecular Nutrition, Emory University School of Medicine, Atlanta, GA 30322; and Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912

⁴To whom correspondence should be addressed. E-mail: tzieg01{at}emory.edu.

Reactive oxygen species (ROS) produced by gut mucosal cells during conditions such as inflammatory bowel disease (IBD) may impair mucosal repair and nutrient transport/absorptive function. Absorption of di- and tripeptides in the small intestine and colon is mediated by the H⁺-dependent transporter PepT1, but effects of oxidative stress on di- and tripeptide transport are unknown. We assessed whether exposure to hydrogen peroxide (H₂O₂) influences dipeptide transport in human colonic epithelial (Caco-2) cells. Uptake of [¹⁴C]glycylsarcosine (Gly-Sar) was used to evaluate PepT1-mediated dipeptide transport. Exposure to 1–5 mmol/L H₂O₂ for 24 h caused a dose-dependent decrease in Gly-Sar transport, which was associated with decreased PepT1 transport velocity (V_max). Treatment with alanylglutamine (Ala-Gln) or growth hormone (GH) did not alter Caco-2 Gly-Sar transport in the absence of H₂O₂. However, both Ala-Gln and GH prevented the decrease in dipeptide transport observed with 1 mmol/L H₂O₂ treatment. Ala-Gln, but not GH, maintained cellular glutathione and prevented the decrease in PepT1 protein expression. Thus, these agents should be further investigated as potential therapies to improve absorption of small peptides in disorders associated with oxidative injury to the gut mucosa.

KEY WORDS: • oxidative stress • glutamine • intestine • redox status

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