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Articles by C Bauchart Thevret
Total Records ( 5 ) for C Bauchart Thevret
  C Bauchart Thevret , B Stoll , S Chacko and D. G. Burrin
 

We recently showed that the developing gut is a significant site of methionine transmethylation to homocysteine and transsulfuration to cysteine. We hypothesized that sulfur amino acid (SAA) deficiency would preferentially reduce mucosal growth and antioxidant function in neonatal pigs. Neonatal pigs were enterally fed a control or an SAA-free diet for 7 days, and then whole body methionine and cysteine kinetics were measured using an intravenous infusion of [1-13C;methyl-2H3]methionine and [15N]cysteine. Body weight gain and plasma methionine, cysteine, homocysteine, and taurine and total erythrocyte glutathione concentrations were markedly decreased (–46% to –85%) in SAA-free compared with control pigs. Whole body methionine and cysteine fluxes were reduced, yet methionine utilization for protein synthesis and methionine remethylation were relatively preserved at the expense of methionine transsulfuration, in response to SAA deficiency. Intestinal tissue concentrations of methionine and cysteine were markedly reduced and hepatic levels were maintained in SAA-free compared with control pigs. SAA deficiency increased the activity of methionine metabolic enzymes, i.e., methionine adenosyltransferase, methionine synthase, and cystathionine β-synthase, and S-adenosylmethionine concentration in the jejunum, whereas methionine synthase activity increased and S-adenosylmethionine level decreased in the liver. Small intestine weight and protein and DNA mass were lower, whereas liver weight and DNA mass were unchanged, in SAA-free compared with control pigs. Dietary SAA deficiency induced small intestinal villus atrophy, lower goblet cell numbers, and Ki-67-positive proliferative crypt cells in association with lower tissue glutathione, especially in the jejunum. We conclude that SAA deficiency upregulates intestinal methionine cycle activity and suppresses epithelial growth in neonatal pigs.

  C Bauchart Thevret , L Cui , G Wu and D. G. Burrin
 

Arginine is an indispensable amino acid in neonates and is required for growth. Neonatal intestinal epithelial cells (IEC) are capable of arginine transport, catabolism, and synthesis and express nitric oxide (NO) synthase to produce NO from arginine. Our aim was to determine whether arginine directly stimulates IEC growth and protein synthesis and whether this effect is mediated via mammalian target of rapamycin (mTOR) and is NO-dependent. We studied neonatal porcine IEC (IPEC-J2) cultured in serum- and arginine-free medium with increasing arginine concentrations for 4 or 48 h. Our results show that arginine enhances IPEC-J2 cell survival and protein synthesis, with a maximal response at a physiological concentration (0.1–0.5 mM). Addition of arginine increased the activation of mTOR, p70 ribosomal protein S6 (p70 S6) kinase, and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) in a time- and dose-dependent manner. The arginine-induced protein synthesis response was not inhibited by the NO inhibitors nitro-l-arginine methyl ester (l-NAME) and aminoguanidine, despite inducible NO synthase expression in IPEC-J2 cells. Moreover, protein synthesis was not increased or decreased in some cases by addition of an NO donor (S-nitroso-N-acetylpenicillamine), arginine precursors (proline and citrulline) in the absence of arginine, or insulin; S-nitroso-N-acetylpenicillamine suppressed phosphorylation of mTOR, p70 S6 kinase, and 4E-BP1. We found a markedly higher arginase activity in IPEC-J2 cells than in primary pig IEC. Furthermore, mTOR inhibition by rapamycin partially (42%) reduced the arginine-induced protein synthesis response and phosphorylation of mTOR and 4E-BP1. We conclude that arginine-dependent cell survival and protein synthesis signaling in IPEC-J2 cells are mediated by mTOR, but not by NO.

 
 
 
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