Effects Of L-Leucine On Intestinal Development And Amino Acid Transport In Breast-fed Piglets

The effects of L-leucine on intestinal development and growth in piglet were investigated through in vitro cell culture studies and in vivo feeding experiments.(1) Intestinal porcine epithelial cells (IPEC-J2) were cultured in DMEM special medium containing0,0.5,1,2,5or10mmol/L L-Leucine for24h. We found that the protein abundances of ATB0,+, ZO-1, ZO-2and Claudin-3were increased when L-leucine was added to the culture medium. The cell number was greater (P<0.05) in the presence of5mmol/L L-leucine, compared with the other groups.(2) Effects of L-leucine supplementation on piglet growth performance and intestinal development (Experiment2). Sixty2.84±0.02kg normal birth weight (NBW) piglets and Sixty intrauterine growth restricted (IUGR) piglets with the body weight of1.88±0.02kg at7days of age were randomly alloted into one of four groups, respectively. The expreiment lasted for2wks. Compared with control piglets, dietary supplementation with0.7,1.4and2.1g/kg BW L-leucine twice daily increased (P<0.05) daily weight gain, and body weight of neonatal piglets with a normal birth weight, but opposite results were obtained for IUGR piglets. L-leucine supplementation improved the development of the small intestine in neonatal NBW piglets.(3) Effects of L-leucine supplementation on amino acid transporters in the small intestine and kidney of neonatal piglets. This experiment was based on Experiment2. In jejunum of NBW piglets, the mRNA levels for of ATB0,+, b0’+AT, B0AT1were significantly increased, and that for y+LAT1was reduced when L-leucine was supplemented. Moreover, the protein abundance of ATB0,+was increased by L-leucine administration. In the jejunum of IUGR neonatal piglets, L-leucine supplementation decreased mRNA levels of y+LAT1, ASCT2and b0,’+AT while increasing that of ATB0>+. In the kidney of IUGR neonatal piglets, administration of L-leucine increased the abundance of xCT protein, but had no effect on the protein abundance of ATB0,+, LAT2, PAT1, rBAT and SNAT2.(4) Effects of L-leucine supplementation on amino acid concentrations in tissues (small intestine, skeletal muscles, liver, and kidney) of breast-fed piglets. This experiment was based on experiment2. L-leucine supplementation had significant effects on the concentrations of glycine, glutamine and glutamate (P<0.05) in longissimum doris of NBW suckling piglets.(5) Effects of L-leucine supplementation on cell signalling pathway related to intracellular protein synthesis and breakdown. This experiment was based on experiment2. L-leucine supplementation increased p-4EBP1,4EBP1/p-4EBP1(P<0.05), but had not influence on p-mTOR, mTOR, p-mTOR/mTOR and4EBP1in thigh muscle of NBW piglets. In skeletal muscle of IUGR breast-fed piglets, L-leucine supplementation increased p-mTOR,4EBP1and p-4EBP1proteins. In addition, L-leucine supplementation significantly decreased expression of the MuRF1gene (P<0.05), and increased mRNA levels for Myf5, MyoD and MyoG in skeletal muscle of NBW piglets (P<0.05). In contrast, L-leucine supplementation decreased gene expression of MuRF1in skeletal muscle of IUGR piglets (P<0.05), but significantly increased the mRNA levels for Atrogin-1and Myf5(P<0.01). Collectively, these results indicate that dietary L-leucine has a regulatory role in nutrition and amino acid transport in young pigs. Effects of L-leucine supplementation depend on its doses, as well as birth weight and tissue type in piglets.