Differential regulation of protein synthesis in skeletal muscle and liver of neonatal pigs by leucine through an mTORC1-dependent pathway

Neonatal growth is characterized by a high protein synthesis rate that is largely due to an enhanced sensitivity to the postprandial rise in insulin and amino acids, especially leucine. The mechanism of leucine＇s action in vivo is not well understood. In this study, we investigated the effect of leucine infusion on protein synthesis in skeletal muscle and liver of neonatal pigs. To evaluate the mode of action of leucine, we used rapamycin, an inhibitor of mammalian target of rapamycin （mTOR） complex-1 （mTORC1）. Overnight-fasted 7-day-old piglets were treated with rapamycin for 1 hour and then infused with leucine （400 μmol·kg^-1·h^-1） for 1 hour. Leucine infusion increased the rate of protein synthesis, and ribosomal protein S6 kinase 1 （S6K1） and eukaryotic initiation factor （elF） 4E-binding protein-1 （4E-BP1） phosphorylation in gastrocnemius and masseter muscles （P 〈 0.05）, but not in the liver. The leucine-induced stimulation of protein synthesis and S6K1 and 4E-BP1 phosphorylation were completely blocked by rapamycin, suggesting that leucine action is by an mTORC1-dependent mechanism. Neither leucine nor rapamycin had any effect on the activation of the upstream mTQRC1 regulators, AMP-activated protein kinase and protein kinase B, in skeletal muscle or liver. The activation of elF2α and elongation factor 2 was not affected by leucine or rapamycin, indicating that these two pathways are not limiting steps of leucine-induced protein synthesis. These results suggest that leucine stimulates muscle protein synthesis in neonatal pigs by inducing the activation of mTORC1 and its downstream pathway leading to mRNA translation.

The effect of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) on fatty acid oxidation in hepatocytes isolated from neonatal piglets

In the present study, the effect of 5-aminoimidazole-4-carboxamide ribonucleoside （AICAR） on long-chain fatty acid oxidation by hepatocytes isolated from suckled neonatal pig liver （a low ketogenic and lipogenic tissue） was tested Incubation of hepatocytes with AICAR （0.5 raM） in the presence of ] mM of carnitine and 10 mM of glucose for 1 hour at 37℃ had no significant effect on total [1-14C]-palrnitate （0.5 mM） oxidation （14CO2 and 14C-Acid soluble products （ASP））. Consistent with the fatty acid oxidation, carnitine palmitoyltransferase I activity and inhibition of its activity by malonyI-CoA （10 MM） assayed in cell homogenate also remained constant. However, addition of AICAR to the hepatocytes decreased 14CO2 production by 18% compared to control （p 〈 0.06）. The reduction of labeled carboxylic carbon accumulated in C02 caused a significant difference in distribution of oxidative products between 14C02 and 14C-ASP （p 〈 0.03） compared with the control. It was also noticed that acetyI-CoA carboxylase （ACC） was increased by AICAR （p 〈 0.03）, indicating that ACC might drive acetyI-CoA toward fatty acid synthesis pathway and induce an increase in distribution of fatty acid carbon to 14C-ASP. Addition of insulin to hepatocyte incubations with AICAR did not change the oxidative product distribution between CO2 and ASP, but further promoted ACC activity. The increased ACC activity was 70% higher than in the control group when citrate was absent in the reaction medium and was 30% higher when citrate was present in the medium. Our results suggest that AICAR may affect the distribution of metabolic products from fatty acid oxidation by changing ACC activity in hepatocyte isolated from suckled neonatal piglets; however, the basis for the increase in ACC activity elicited by AICAR is not apparent.

Risk Factors for Prevalence of Enterotoxigenic Escherichia coli (ETEC) in Diarrheic and Non-diarrheic Neonatal and Weaner Pigs, South Africa

Enterotoxigenic Escherichio coli （ETEC） causes neonatal and post-weaning diarrhea in pigs. In order to determine the risk factors, rectal/fecal swabs and visceral organs obtained from pig farms in two regions of South Africa were analyzed microbiologically against risk variables. Seventy-two percent of young pigs were found to be positive for ETEC toxin genes; estB （38.9%）, estB/STAP （25%）, and estB/LT （13.9%） were dominant. Risk factors for ETEC-diarrhea in pigs include： leaving sick piglets in a pen with healthy piglets [odds ratio （OR） = 33.52; P 〈 0.0001]; water spillage in pen （OR = 42.87; P 〈 0.0001）; hypothermic piglets （OR = 7.29; P 〈 0.0001）; runt piglets in pen with healthy littermates （OR = 3.65; P 〈 0.0001）; and prolonged use of antibiotics （OR = 3.05; P = 0.05）.

Increased maternal consumption of methionine as its hydroxyl analog promoted neonatal intestinal growth without compromising maternal energy homeostasis

Background： To determine responses of neonatal intestine to maternal increased consumption of DL-methionine（DLM） or DL-2-hydroxy-4-methylthiobutanoic acid（HMTBA）, eighteen primiparous sows（Landrace × Yorkshire） were allocated based on body weight and backfat thickness to the control, DLM and HMTBA groups（n = 6）, with the nutritional treatments introduced from postpartum d0 to d14.Results： The DLM-fed sows showed negative energy balance manifested by lost bodyweight, lower plasma glucose, subdued tricarboxylic acid cycle, and increased plasma lipid metabolites levels. Both villus height and ratio of villus height to crypt depth averaged across the small intestine of piglets were higher in the DLM and HMTBA groups than in the control group. Piglet jejunal oxidized glutathione concentration and ratio of oxidized to reduced glutathione were lower in the HMTBA group than in the DLM and control groups. However, piglet jejunal aminopeptidase A, carnitine transporter 2 and IGF-II precursor m RNA abundances were higher in the DLM group than in the HMTBA and control groups.Conclusion： Increasing maternal consumption of methionine as DLM and HMTBA promoted neonatal intestinal growth by increasing morphological development or up-regulating expression of genes responsible for nutrient metabolism. And increasing maternal consumption of HMTBA promoted neonatal intestinal antioxidant capacity without compromising maternal energy homeostasis during early lactation.

EXPERIMENTAL AND CLINICAL STUDY ON BILIRUBIN NEUROTOXICITY DETECTED BY VISUAL EVOKED POTENTIALS TO FLASH

Objective Evaluate the sensitivity and reliability of visual evoked potential to flash (F-VEP) in detecting bilirubin neurotoxicity and approach the risk parameters of bilirubin neurotoxicity in hyper-bilirubinemia newborns. Methods Based on the successful establishment of animal models for acute bilirubin encephalopathy by intraperitoneal infusion of bilirubin with a dosage of 100～200μg/g body weight to 1-week-old guinea pigs, the F-VEP was recorded in animal models and human neonates with hyperbilirubinemia, and the sensitivity and reliability of F-VEP in detecting bilirubin neurotoxicity were evaluated. Results F-VEP features and its P1 latency significantly correlated to brain adenosine triphosphate (ATP) level, neurobeha-vioral and neuropathological changes in experimental bilirubin encephalopathy; neonates with hyperbiliru-binemia showed significant F-VEP changes characterized by absence of P1 or P1 latency prolonged in 1～7-day-old newborns, especially when the jaundice was caused by immun oincompatibility and infectious diseases. Conclusion F-VEP would be a good discriminator for bilirubin neurotoxicity, and can become a promising technique in monitoring bilirubin encephalopathy.