Important Roles For Glycine In Piglet Growth And Intestinal Function

The important roles of glycine in piglet growth and intestinal function were investigated through three in vitro cell culture studies and two in vivo feeding studies.(1) Intestinal porcine epithelial cells (IPEC-1) were cultured (2×106) in1mL Krebs buffer (pH7.4) containing0,0.1,0.25,0.5,1or2mmol/L glycine and2R105Bq [U-14C]glycine (or [U-14C]serine) for2h. We found that less than10%of the glycine utilized by the cells was converted into serine, and only a small quantity of glycine was oxidized to CO2in IPEC-1cells. In contrast, a substantial amount (-80%) of glycine was converted into protein.(2) Effects and mechanisms of glycine on proliferation and protein turnover in IPEC-1cells. IPEC-1cells were cultured in the presence of0,0.1,0.25,0.5,1or2mmol/L glycine. The cell number, protein turnover, and the phosphorylation of Akt、mTOR、P70S6K and4E-BP1were greater (P<0.05) in the presence of1mmol/L glycine, compared with the other groups.(3) The antioxidative effects of glycine on IPEC-1cells and its mechanisms. IPEC-1cells were pretreated with0,0.25or1mmol/L glycine for8h, and then treated with30μmol/L4-hydroxynonenal (4-HNE) for another8h. Pretreated with1mmol/L glycine attenuated their death and apoptosis induced by HNE, which was due to promoting synthesis of reduced glutathione (GSH) and expression of glycine transporter I (GLYT1), as well as reducing the activation of ERK, JNK and p38in the Mitogen-activated protein kinase (MAPK) signaling pathway.(4) Effects of glycine supplementation of milk replacer on piglet nutrition and intestinal development. Sixty newborn piglets at14days of age were randomly alloted into one of four groups. Compared with control piglets, dietary supplementation with0.5,1and2%glycine increased (P <0.05) plasma concentrations of glycine, serine and GSH, daily weight gain, and body weight, while reducing plasma concentrations of ammonia, urea, and glutamine, in a dose-dependent manner. Dietary supplementation with0.5,1and2%glycine enhanced (P<0.05) small-intestinal villus development, glycine transport (measured using Ussing chambers), mRNA levels for GLYT1, and intestinal anti-oxidative capacity.(5) The effects of dietary glycine supplementation on growth of weaned piglets. Ninety-six piglets weaned at28d of age with an average initial body weight of8.23±0.34kg, were randomly alloted into one of four groups. Compared with control piglets, dietary supplementation with1and2%glycine increased (P<0.05) plasma concentrations of glycine, serine and GSH, daily weight gain, and feed effeciency, while reducing plasma concentrations of glutamine, ammonia and urea (P<0.05). In conclusion, glycine can enhance cell growth and proliferation and inhibit oxidative stress in IPEC-1cells. In vivo, dietary glycine can promote growth and intestinal development in newborn piglets and improve growth performance in weaned piglets. These novel results indicate, for the first time, that neither the small intestine nor the whole body can synthesize sufficiently glycine to support optimal growth and metabolic needs and that glycine is a nutritionally essential amino acid for maximal growth of young pigs. The findings not only enhance understanding of protein nutrition, but also have important implications for designing improved formulas for feeding neonatal and weaned piglets.