Leucine Administration in Conjunction With Continuous Feeding Improves Lean Growth in a Preterm Piglet Model

Objectives

Previous work in our lab showed that continuous feeding blunts muscle protein synthesis compared to intermittent bolus feeding in neonatal pigs born at term (a highly translatable model for the human neonate). However, continuous feeding is still indicated in some infants due to feeding intolerance. Our lab has demonstrated that leucine acts as a nutrient signal to stimulate protein synthesis and that intermittent parenteral leucine (Leu) pulses during continuous orogastric feeding increases skeletal muscle mTORC1 signaling and protein synthesis in neonatal pigs born at term. We hypothesized that leucine pulsing during continuous feeding enhances mTORC1 signaling to protein synthesis and lean growth in a preterm piglet model.

Methods

Pigs delivered by cesarean section at 105 d gestation were gradually transitioned over 7 d from parenteral to enteral feeding, via an orogastric tube, and continuously fed a protein and energy balanced milk-replacer diet (ME = 195 kcal/kg/d; Protein = 13.5 g/kg/d) for the remainder of the study (17 d). Pigs were randomly assigned to either: 1) Leu (LEU; 1.6 mmol/kg bodyweight/4 h; n = 4) or Alanine (ALA; 1.6 mmol Ala/kg bodyweight/4 h; isonitrogenous control; n = 4) groups. The assigned amino acid solution was administered i.v.as a “pulse” for 1 h, every 4 h from day 3 to day 24 of study. Body composition was determined via dual x-ray absorptiometry on day 22 and indices of amino acid signaling and mTORC1 activation were determined postprandially, 60 min after initiation of the last pulse on day 24.

Results

LEU pigs had a higher average daily gain (ADG) (P < 0.05) and 13% higher final body weight than ALA pigs (P < 0.05). Total lean mass tended to be higher (+13%; P < 0.06) in LEU compared to ALA, while body fat percentage remained statistically unchanged. Longissimus dorsi muscle weight was 17% heavier in LEU than ALA pigs (P = 0.01). Indices of mTORC1 activation, i.e., phosphorylation of S6K1 and 4EBP1 and abundance of the eIF4E-eIF4G complex, were increased in longissimus dorsi and gastrocnemius muscle of LEU compared to ALA pigs.

Conclusions

These results show that leucine supplementation during continuous feeding enhances mTORC1-activated translation initiation in skeletal muscle and was associated with an increase in lean growth and weight gain in a preterm piglet model.

Funding Sources

USDA NIH.

Parenteral lipid emulsions induce unique ileal fatty acid and metabolomic profiles but do not increase the risk of necrotizing enterocolitis in preterm pigs

Necrotizing enterocolitis (NEC) is a manifestation of maladaptive intestinal responses in preterm infants centrally medicated by unattenuated inflammation. Early in the postnatal period, preterm infants develop a deficit in arachidonic and docosahexaenoic acid, both potent regulators of inflammation. We hypothesized that the fatty acid composition of parenteral lipid emulsions uniquely induces blood and intestinal fatty acid profiles which, in turn, modifies the risk of NEC development. Forty-two preterm pigs were randomized to receive one of three lipid emulsions containing 100% soybean oil (SO), 15% fish oil (MO15), or 100% fish oil (FO100) with enteral feedings over an 8-day protocol. Blood and distal ileum tissue were collected for fatty acid analysis. The distal ileum underwent histologic, proteomic, and metabolomic analyses. Eight pigs [3/14 SO (21%), 3/14 MO15 (21%), and 2/14 FO100 (14%)] developed NEC. No differences in NEC risk were evident between groups despite differences in induced fatty acid profiles in blood and ileal tissue. Metabolomic analysis of NEC versus no NEC tissue revealed differences in tryptophan metabolism and arachidonic acid-containing glycerophospholipids. Proteomic analysis demonstrated no differences by lipid group; however, 15 proteins differentiated NEC versus no NEC in the domains of tissue injury, glucose uptake, and chemokine signaling. Exposure to parenteral lipid emulsions induces unique intestinal fatty acid and metabolomic profiles; however, these profiles are not linked to a difference in NEC development. Metabolomic and proteomic analyses of NEC versus no NEC intestinal tissue provide mechanistic insights into the pathogenesis of NEC in preterm infants.NEW & NOTEWORTHY Exposure to parenteral lipid emulsions induces unique intestinal fatty acid and metabolomic profiles; however, these profiles are not linked to a difference in NEC risk in preterm pigs. Metabolomic and proteomic analyses provide mechanistic insights into NEC pathogenesis. Compared with healthy ileal tissue, metabolites in tryptophan metabolism and arachidonic acid-containing glycerophospholipids are increased in NEC tissue. Proteomic analysis differentiates NEC versus no NEC in the domains of tissue injury, glucose uptake, and chemokine signaling.

Comparison of High Fructose Corn Syrup Versus Sucrose Consumption on Non-Alcoholic Fatty Liver Disease in Juvenile Iberian Pigs

Objectives

Non-alcoholic fatty liver disease (NAFLD) is a chronic metabolic disorder and the most common liver disease in pediatric populations. Epidemiological studies have observed a parallel increase in fructose consumption and incidence of NAFLD among children. The objective of this study was to compare the relative effect of inclusion of isocaloric amounts of high fructose corn syrup (66.5% fructose, 33.5% glucose) versus sucrose (50% fructose, 50% glucose) in the diet for 16 weeks on endpoints of NAFLD and insulin resistance.

Methods

30-d-old Iberian pigs were housed in pairs and randomly assigned to receive solid diets (g/kg body weight × d) of 1) control (CON; n = 6): 0 g HFCS, 0 g SUC, and 174.03 kcal metabolizable energy (ME), 2) high-fructose corn syrup (HFCS; n = 8): 31.20 g high-fructose corn syrup, 0 g sucrose and 261 kcal ME, and 3) Sucrose (SUC; n = 6): 0 g high-fructose corn syrup, 24.04 g sucrose and 261 kcal ME for 16 consecutive weeks.

Results

Compared to CON, both HFCS and SUC diets increased body weight gain (P ≤ 0.001), relative liver weight (P ≤ 0.01) and leptin levels (P ≤ 0.01), and decreased percentage of lean mass composition in the animals (P ≤ 0.001). In addition, HFCS increased fasting insulin levels compared to CON (P ≤ 0.05), and decreased percentage lean mass compared to SUC (P ≤ 0.05). 75% of HFCS and 66.6% of SUC pigs showed histopathological lesions consistent with microvesicular steatosis with periportal or diffuse distribution. Serum markers of liver injury did not differ between diets, and none of the animals developed inflammation, hepatocellular ballooning, Mallory hyaline or necrosis in the liver. Metabolomics analysis revealed liver sorbitol and monosaccharide concentrations were higher in both the HFCS and SUC groups versus CON (P ≤ 0.05), while adenosine monophosphate (AMP) were higher and adenosine diphosphate levels lower in the HFCS and SUC in comparison to CON (P ≤ 0.05). Numerous phosphatidylcholines and sphingomyelins were differentially changed in the HFCS group versus CON (P ≤ 0.05).

Conclusions

Feeding diets high in either sucrose or high fructose corn syrup promoted obesity and steatosis in the animals. Further research is needed to investigate the mechanisms leading to increased insulin resistance in the HFCS group.

Funding Sources

ARI #58,873, AcornSeekers, STRIDE.

Use of a novel docosahexaenoic acid formulation vs control in a neonatal porcine model of short bowel syndrome leads to greater intestinal absorption and higher systemic levels of DHA

Infants with short bowel syndrome (SBS) are at high risk for malabsorption, malnutrition, and failure to thrive. The objective of this study was to evaluate in a porcine model of SBS, the systemic absorption of a novel enteral Docosahexaenoic acid (DHA) formulation that forms micelles independent of bile salts (DHA-ALT®). We hypothesized that enteral delivery of DHA-ALT® would result in higher blood levels of DHA compared to a control DHA preparation due to improved intestinal absorption. SBS was induced in term piglets through a 75% mid-jejunoileal resection and the piglets randomized to either DHA-ALT® or control DHA formulation (N=5 per group) for 4 postoperative days. The median±IQR difference in final vs starting weight was 696±425 g in the DHA-ALT® group compared to 132±278 g in the controls (P=.08). Within 12 hours, median±IQR DHA and eicosapentaenoic acid plasma levels (mol%) were significantly higher in the DHA-ALT® vs control group (4.1±0.3 vs 2.5±0.5, P=.009; 0.7±0.3 vs 0.2±0.005, P=.009, respectively). There were lower fecal losses of DHA and greater ileal tissue incorporation with DHA-ALT® vs the control. Morphometric analyses demonstrated an increase in proximal jejunum and distal ileum villus height in the DHA-ALT® group compared to controls (P=.01). In a neonatal porcine model of SBS, enteral administration of a novel DHA preparation that forms micelles independent of bile salts resulted in increased fatty acid absorption, increased ileal tissue incorporation, and increased systemic levels of DHA.

Digestive physiology of the pig symposium: intestinal bile acid sensing is linked to key endocrine and metabolic signaling pathways

Bile acids have historically been considered to mainly function in cholesterol homeostasis and facilitate fat digestion in the gastrointestinal tract. Recent discoveries show that bile acids also function as signaling molecules that exert diverse endocrine and metabolic actions by activating G protein-coupled bile acid receptor 1 (GPBAR1/G-protein-coupled bile acid receptor 1 or TGR5), a membrane G protein-coupled receptor, and farnesoid X receptor (FXR), a member of the nuclear hormone receptor superfamily. These bile acid sensing receptors are expressed in intestinal epithelial cells, TGR5 in enteroendocrine cells and FXR in enterocytes, which line the mucosa of gut lumen. A dominant effect of intestinal FXR activation by bile acids is secretion of fibroblast growth factor (FGF) 19, a novel enterokine that functions as a central enterohepatic signal to maintain bile acid homeostasis in the liver. Activation of TGR5 on enteroendocrine cells stimulates secretion of glucagon-like peptides (GLP)-1 and -2, which function, respectively, as the major incretin hormone involved in glucose homeostasis and key trophic hormone in intestinal adaptation and growth in response to food ingestion. The biological actions induced by bile acid activation of intestinal FXR and TGR5 have important therapeutic implications for the pathogenesis and treatment of several metabolic diseases, such as cholestasis and diabetes. This review highlights these new developments in the biology of intestinal bile acid sensing and metabolic function and discusses the potential implications for the health and agricultural production of domestic swine.

Near-infrared spectroscopy measurement of abdominal tissue oxygenation is a useful indicator of intestinal blood flow and necrotizing enterocolitis in premature piglets

PURPOSE

A major objective of necrotizing enterocolitis (NEC) research is to devise a noninvasive method of early detection. We hypothesized that abdominal near-infrared spectroscopy (A-NIRS) readings will identify impending NEC in a large animal model.

METHODS

Piglets were prematurely delivered and received parenteral nutrition followed by enteral feedings. Serial A-NIRS readings were obtained for 5 days, and animals were monitored for NEC. Separately, A-NIRS readings were obtained in healthy piglets to validate the correlation of A-NIRS with splanchnic oxygen delivery.

RESULTS

Of 29 piglets, 3 developed NEC. Eleven piglets without NEC died prematurely. Fifteen piglets remained healthy, had normal histologic assessment of their intestines, and served as controls. Abdominal near-infrared spectroscopy readings within 12 hours of birth were significantly lower in animals that developed NEC compared with healthy littermates (4% vs 33%, P = .02). For all time-points measured, A-NIRS readings were significantly lower in the NEC group compared with controls (21% vs 55%, P < .001). Abdominal near-infrared spectroscopy readings correlated with both decreased pulse oximetry readings during apneic episodes (r = 0.96) and increased superior mesenteric artery flow in response to glucagon-like peptide 2 (r = 0.67).

CONCLUSION

Abdominal near-infrared spectroscopy is capable of detecting alterations in intestinal oxygenation and perfusion in neonatal piglets and may allow early detection of neonates at risk for NEC.

Chronic protein deficiency differentially affects the kinetics of plasma proteins in young pigs

The use of plasma protein concentrations to assess protein-nutritional status has been questioned because concentrations and kinetics are affected by factors other than protein intake. To determine the effect of protein deficiency on plasma protein concentration and synthesis, two groups of four piglets consumed diets containing either 20 or 3% protein. After 8 wk, 2H3-leucine was infused intravenously to measure the fractional and absolute synthesis rates (FSR and ASR) of albumin, transferrin, retinol binding protein (RBP), transthyretin (TTR), a new peptide called TTR2, the high density apolipoprotein (HDL-apoA-1), fibrinogen, and haptoglobin. Compared with controls, protein-deficient pigs had significantly lower (P < 0.05) plasma albumin, RBP and TTR2 concentrations, significantly slower (P < 0.05) FSR of fibrinogen, HDL-apoA-1, transferring and TTR2, significantly lower (P < 0.05) ASR of albumin, fibrinogen, transferrin, and TTR2, and a significantly higher (P < 0.05) ASR of TTR. Fibrinogen and transferrin concentrations did not differ between groups, but transthyretin concentration was higher in protein-deficient pigs. These results suggest that protein-nutritional status cannot be predicted from the concentrations of all plasma proteins, that chronic protein deficiency affects the rate of synthesis of only some plasma proteins, and that the kinetic response of plasma proteins to protein restriction cannot be predicted from measurements of plasma concentrations.

Growth and metabolism of gastrointestinal and skeletal muscle tissues in protein-malnourished neonatal pigs

Our objective was to determine whether neonates adapt to protein malnutrition by preserving the relative growth and metabolism of gastrointestinal tissue at the expense of skeletal muscle. We measured gastrointestinal, liver, and carcass tissue masses and blood flow, oxygen consumption, and net glucose and amino acid fluxes in vivo of the portal-drained visceral tissues (PDV) in neonatal pigs fed isocaloric diets containing either 30% protein [control (C)] or 15% [low protein (LP)] for 14 days. Relative protein mass and fasting blood flow and oxygen consumption of PDV tissue in either group were not different. Relative protein mass of liver and carcass was lower in LP pigs. Net essential amino acid absorption and insulin concentration after feeding were lower in LP pigs. Results demonstrate that protein malnutrition in neonatal pigs differentially altered rates of tissue growth, such that the proportion of body protein partitioned into gastrointestinal tissue was preserved, while that of skeletal muscle was reduced. Chronic reduction in amino acid absorption in protein-malnourished pigs resulted in a reduced insulin response to feeding, which presumably limited substrate availability and the anabolic stimulus for skeletal muscle protein accretion.