Increased Circulating Cortisol After Vaginal Birth Is Associated With Increased FGF19 Secretion in Neonatal Pigs

The influence of birth modality (scheduled cesarean or spontaneous vaginal) on the development of the newborn has been a source of controversy in neonatology. The impact of cesarean vs vaginal birth on the development of bile acid and fibroblast growth factor 19 (FGF19) signaling is unknown. Our aim was to determine the effect of birth modality and gestational age (preterm vs term) on plasma hormone levels, bile acid pool distribution, expression of genes in the bile acid-FXR-FGF19 pathway, and plasma levels of FGF19 at birth and on day 3 of life in neonatal pigs. Four sows underwent cesarean delivery on gestation day 105 (n = 2) and 114 (n = 2; term = 115 days), and 2 additional sows were allowed to farrow at term (gestation days 112 and 118). Piglets were euthanized at birth (Term-Vaginal n = 6; Term-Cesarean n = 8; Preterm n = 10) for tissue and blood collection, and the remaining pigs received total parenteral nutrition then were fed enterally on day 3 (Term-Vaginal n = 8; Term-Cesarean n = 10; Preterm n = 8), before blood and tissue were collected. Piglets born vaginally had a markedly (30-fold) higher plasma FGF19 at birth than term pigs born via cesarean delivery, and 70-fold higher than preterm pigs (P < 0.001). However, distal ileum FGF19 gene expression was similar in all groups (P > 0.05). Plasma FGF19 positively correlated with plasma cortisol (r = 0.58; P < 0.05) and dexamethasone treatment increased ileal FGF19 expression in cultured pig tissue explants and human enteroids. Our findings suggest that exposure to maternal or endogenous glucocorticoids in the perinatal period may upregulate the development of the bile acid-FGF19 pathway.

137 Standing in the gap of Neonatal Microbe-Host Barrier Function

The provision of mammary secretions in the form of colostrum and mature milk for newborns is an essential survival function that has evolved over millennia in mammalian species. Colostrum serves a vital function for neonates by providing nutrients for energy and growth as they transition from placental nutrition to oral ingestion of more complex macromolecules, including lactose, proteins, and triglycerides. Colostrum also provides critical immune protection from colonizing commensal and pathogenic microbes that supports neonatal immunity until maturation of the immune system. This concept of homologous passive immunity conferred by colostrum is well known in farm animal species and has been largely attributed to immunoglobulins transferred from mother to offspring. Heterologous passive immunity is also an approach whereby bovine colostrum obtained from normal or hyperimmunized cows is used therapeutically to prevent specific GI diseases in swine and human infants. The critical importance of colostrum to survival of newborn farm animals also holds true in the prevention of intestinal diseases, such as necrotizing enterocolitis (NEC), in hospitalized premature infants. In preterm infants, mother’s own milk may not always be available and infants are instead fed donor human milk, which provides effective protection against NEC. Whether the benefits of human milk in the prevention of NEC are due to immunoglobulins is not well established. These scenarios whereby colostrum from different species or different mothers within a species protect the neonatal gut point to common elements of host protection. New experimental approaches and tools are being applied to understanding the molecular mechanism of how components of maternal milk impact gut microbial colonization and interaction with the host immune system.

Fibroblast growth factor 15/19 expression, regulation, and function: An overview

Since the discovery of fibroblast growth factor (FGF)-19 over 20 years ago, our understanding of the peptide and its role in human biology has moved forward significantly. A member of a superfamily of paracrine growth factors regulating embryonic development, FGF19 is unique in that it is a dietary-responsive endocrine hormone linked with bile acid homeostasis, glucose and lipid metabolism, energy expenditure, and protein synthesis during the fed to fasted state. FGF19 achieves this through targeting multiple tissues and signaling pathways within those tissues. The diverse functional capabilities of FGF19 is due to the unique structural characteristics of the protein and its receptor binding in various cell types. This review will cover the current literature on the protein FGF19, its target receptors, and the biological pathways they target through unique signaling cascades.

Depletion and enrichment of phytosterols in soybean oil lipid emulsions directly associate with serum markers of cholestasis in preterm parenteral nutrition-fed pigs

BACKGROUND

Clinical reports show a positive correlation between phytosterol concentrations and severity of cholestatic liver disease markers in infants during long-term administration of parenteral lipid emulsions. Establishing a causal link between phytosterols and cholestasis has been complicated by confounding factors of lipid emulsion load, fatty acid composition, and vitamin E in many of these studies. The goal of this study is to determine whether altering the phytosterol concentration within a common soybean oil-based emulsion will alter the onset and severity of cholestasis in parenterally fed preterm piglets.

METHODS

Preterm piglets were administered, for 21 days, either enteral nutrition (ENT) or parenteral nutrition (PN) prepared from a soybean oil-based emulsion containing either 24.0% (depleted [DEP]), 100% (Intralipid; normal phytosterol [NP] concentration), or 144% (enriched [ENR]) total phytosterol concentration.

RESULTS

At the end of the study, plasma and liver phytosterol concentrations were highest in the ENR group, followed by NP and then DEP and ENT. Serum direct bilirubin, serum bile acids, and γ-glutamyltransferase were higher in the ENR and NP groups compared with either DEP or ENT groups. All PN lipid groups showed evidence of mild hepatic steatosis but no change in hepatic expression of proinflammatory cytokines or Farnesoid X receptor target genes.

CONCLUSION

The increase in serum direct bilirubin was lower in the DEP group vs the lipid emulsions with normal or ENR phytosterols. Our results provide additional evidence that phytosterols are linked to an increase in serum markers of cholestasis in preterm PN-fed pigs.

191 Pulsatile Administration of Leucine Promotes mTOR Signaling and Protein Synthesis in Skeletal Muscle of Continuously Fed Preterm Pigs

Continuous feeding does not elicit an optimal anabolic response but is required for some premature infants. We reported previously that intermittent intravenous pulses of Leu (800 μmol Leu·kg-1·h-1 every 4 h) to continuously fed pigs born at term enhanced skeletal muscle mTOR signaling and protein synthesis (PS). The objective of this study was to determine if the anabolic response of skeletal muscle to intermittent Leu pulses is altered following premature birth. Pigs delivered 10 d preterm by cesarean section were advanced to full oral feeding over four days (195 kcal·kg-1·d-1; 13.5 g protein·kg-1·d-1). Pigs were assigned to 1 of 4 treatments: 1) ALA (continuous feeding; 800 μmol Ala·kg-1·h-1 every 4 h; n = 7); 2) L1× (continuous feeding; 800 μmol Leu·kg-1·h-1 every 4 h; n = 6); 3) L2× (continuous feeding; 1600 μmol Leu·kg-1·h-1 every 4 h; n = 6); and 4) INT (intermittent feeding every 4 h; n = 5). Pigs received a Phe tracer 30 min following the amino acid pulse or intermittent feeding to measure PS in longissimus dorsi muscle. Anabolic signaling downstream of mTOR was determined by immunoblot.ResultsPS was higher in L2× and INT compared to ALA (P &lt; 0.05) but was not different between L2× and INT; PS in L1× was intermediate and not different from other groups. Phosphorylation of 4EBP1 and S6K1 was higher in INT compared to L1× and ALA groups (P &lt; 0.05) but was not different compared to L2×. Phosphorylation of 4EBP1, but not S6K1, was higher in L2× compared to ALA (P &lt; 0.05); phosphorylation of 4EBP1 and S6K1 was not different between L1× and L2×.ConclusionsThese results demonstrate that intravenous Leu enhances mTOR activation and PS in LD muscle of continuously fed preterm pigs. However, the amount required may be higher than in pigs born at term.Source of Research SupportNIH and USDA.

Intermittent Leucine Pulses Enhance Skeletal Muscle mTOR Signaling and Protein Synthesis in Continuously Fed Preterm Pigs

Objectives

Extrauterine growth restriction in premature infants is associated with reduced lean mass and long-term morbidities. We have reported previously that intermittent parenteral pulses of Leu promote skeletal muscle mTOR signaling and protein synthesis of continuously fed neonatal pigs born at term. The objective of this study was to determine the effect of prematurity on the response of skeletal muscle anabolic pathways to intermittent parenteral Leu pulses in continuously fed pigs.

Methods

Pigs delivered 10 d preterm by C-section were fitted with jugular vein and carotid artery catheters and an orogastric feeding tube. Pigs were advanced from parenteral to enteral feeding over 4 d (195 kcal · kg−1 · d−1; 13.5 g protein · kg−1 · d−1). On day 4, pigs were assigned to 1 of 4 treatments: 1) ALA (continuous feeding, 7.5 mL · kg−1 · h−1; 800 μmol Ala · kg−1 · h−1 every 4 h; n = 7); 2) L1 × (continuous feeding; 800 μmol Leu · kg−1 · h−1 every 4 h; n = 6); 3) L2 × (continuous

feeding; 1600 μmol Leu · kg−1 · h−1 every 4 h; n = 6); and 4) INT (intermittent feeding; 30 mL · kg−1 fed over 15 min every 4 h; n = 5). On day 5, pigs received L-[ring-2H5]-Phe 30 min after starting the pulse (groups 1, 2, and 3) or meal feeding (group 4). Pigs were euthanized 30 min after isotope injection and longissimus dorsi muscle was collected. Protein synthesis was determined by LC/MS-MS. Indices of amino acid signaling and mTOR activation were determined by immunoprecipitation and immunoblot assays.

Results

Skeletal muscle protein synthesis was higher in L2 × (+37%) and INT (+31%) compared to ALA (P &lt; 0.05), but was not different between L2 × and INT; protein synthesis in L1 × was intermediate and not different from all other groups. The phosphorylation of 4EBP1, downstream of mTOR, was higher in L2 × and INT compared to ALA (P &lt; 0.05), whereas 4EBP1 phosphorylation in L1 × was lower compared to INT (P &lt; 0.05) but not different compared to ALA and L2 × . The abundance of mTOR · RagA complex, upstream of mTOR and activated in response to Leu, was higher in L2 × and INT compared to ALA and L1 × (P &lt; 0.05).

Conclusions

These results show that parenteral Leu can enhance anabolic signaling and protein synthesis in skeletal muscle during continuous feeding in preterm pigs, but the dose required is higher than in pigs born at term.

Funding Sources

Research was supported by NIH and USDA.

Translational Advances in Pediatric Nutrition and Gastroenterology: New Insights from Pig Models

Pigs are increasingly important animals for modeling human pediatric nutrition and gastroenterology and complementing mechanistic studies in rodents. The comparative advantages in size and physiology of the neonatal pig have led to new translational and clinically relevant models of important diseases of the gastrointestinal tract and liver in premature infants. Studies in pigs have established the essential roles of prematurity, microbial colonization, and enteral nutrition in the pathogenesis of necrotizing enterocolitis. Studies in neonatal pigs have demonstrated the intestinal trophic effects of akey gut hormone, glucagon-like peptide 2 (GLP-2), and its role in the intestinal adaptation process and efficacy in the treatment of short bowel syndrome. Further, pigs have been instrumental in elucidating the physiology of parenteral nutrition-associated liver disease and the means by which phytosterols, fibroblast growth factor 19, and a new generation of lipid emulsions may modify disease. The premature pig will continue to be a valuable model in the development of optimal infant diets (donor human milk, colostrum), specific milk bioactives (arginine, growth factors), gut microbiota modifiers (pre-, pro-, and antibiotics), pharmaceutical drugs (GLP-2 analogs, FXR agonists), and novel diagnostic tools (near-infrared spectroscopy) to prevent and treat these pediatric diseases.

Continuous Feeding Does Not Blunt Satellite Cell Abundance, Myonuclear Accretion, or Lean Growth in a Neonatal Piglet Model of Prematurity

Objectives

Lean growth in preterm neonates is poor and may increase the lifelong risk for adverse health outcomes. Strategies are needed to promote skeletal muscle growth in the postnatal period. Skeletal muscle growth, which accounts for the largest fraction of lean mass accretion, requires the coordinated activation of protein synthesis, satellite cell (SC; muscle stem cell) proliferation, differentiation, and fusion into muscle fibers. The objective of this study was to determine the effect of feeding modality on SC abundance, myonuclear accretion, and lean growth in preterm neonatal pigs.

Methods

Pigs delivered 10 d preterm by C-section (952 ± 205 g) were fitted with an umbilical artery catheter (later replaced with jugular vein catheter) and an orogastric tube for parenteral and enteral nutrition, respectively. Pigs were assigned to continuous (CONT; n = 14; 7.5 mL/[kg·h]) or intermittent bolus (INT; n = 30; 30 mL/kg every 4 h) feeding for 21 d (210 kcal/kg and 16 g protein/kg per d); pigs were advanced from parenteral to enteral feeding over 6 d. Bromodeoxyuridine (BrdU; 25 mg·kg−1) was administered to pigs every 12 h from days 19 to 20, inclusive, to label proliferating cells. Body composition was measured by DXA on day 21. Satellite cell (Pax7+) abundance, myonuclear accretion, and muscle fiber cross-sectional area (CSA) were quantified in the longissimus dorsi muscle by immunofluorescence.

Results

Sublaminal Pax7+ SC abundance was similar between CONT and INT groups (60.9 vs. 58.3 ± 6.0 per 1000 fibers). The proportion of sublaminal relative to total Pax7+ SCs was similar between CONT and INT groups (78.8 vs. 78.8 ± 2.2%). The abundance of BrdU + myonuclei, an index of myonuclear accretion, did not differ between CONT and INT groups (26.7 vs. 26.7 ± 3.4 per 1000 fibers). Total myonuclei did not differ between CONT and INT groups (420 vs. 403 ± 16 per 1000 fibers). Muscle fiber CSA did not differ between CONT and INT groups (210 vs. 237 ± 15 µm2). Lean and fat masses were similar between groups.

Conclusions

Unlike term pigs, CONT feeding does not blunt lean growth in preterm pigs compared to INT feeding. The absence of increased lean growth with INT feeding is consistent with the similar SC abundance, myonuclear accretion, and muscle fiber CSA between feeding modalities.

Funding Sources

Research was supported by NIH and USDA.

Nutrient Restriction has Limited Short-Term Effects on Gut, Immunity, and Brain Development in Preterm Pigs

BACKGROUND

Extrauterine growth restriction (EUGR) in preterm infants is associated with higher morbidity and impaired neurodevelopment. Early nutrition support may prevent EUGR in preterm infants, but it is not known if this improves organ development and brain function in the short and long term.

OBJECTIVE

Using pigs as models for infants, we hypothesized that diet-induced EUGR impairs gut, immunity, and brain development in preterm neonates during the first weeks after birth.

METHODS

Forty-four preterm caesarean-delivered pigs (Danish Landrace × Large White × Duroc, birth weight 975 ± 235 g, male:female ratio 23:21) from 2 sows were fed increasing volumes [32-180 mL/(kg·d)] of dilute bovine milk (EUGR group) or the same diet fortified with powdered bovine colostrum for 19 d (CONT group, 50-100% higher protein and energy intake than the EUGR group).

RESULTS

The EUGR pigs showed reduced body growth (-39%, P < 0.01), lower plasma albumin, phosphate, and creatine kinase concentrations (-35 to 14%, P < 0.05), increased cortisol and free iron concentrations (+130 to 700%, P < 0.05), and reduced relative weights of the intestine, liver, and spleen (-38 to 19%, all P < 0.05). The effects of EUGR on gut structure, function, microbiota, and systemic immunity were marginal, although EUGR temporarily increased type 1 helper T cell (Th1) activity (e.g. more blood T cells and higher Th1-related cytokine concentrations on day 8) and reduced colon nutrient fermentation (lower SCFA concentration; -45%, P < 0.01). Further, EUGR pigs showed increased relative brain weights (+19%, P < 0.01), however, memory and learning, as tested in a spatial T-maze, were not affected.

CONCLUSION

Most of the measured organ growth, and digestive, immune, and brain functions showed limited effects of diet-induced EUGR in preterm pigs during the first weeks after birth. Likewise, preterm infants may show remarkable physiological adaptation to deficient nutrient supply during the first weeks of life although early life malnutrition may exert negative consequences later.

Parenteral lipids shape gut bile acid pools and microbiota profiles in the prevention of cholestasis in preterm pigs

Multi-component lipid emulsions, rather than soy-oil emulsions, prevent cholestasis by an unknown mechanism. Here, we quantified liver function, bile acid pools, and gut microbial and metabolite profiles in premature parenterally fed pigs given a soy-oil lipid emulsion, Intralipid (IL), a multi component lipid emulsion, SMOFlipid (SMOF), a novel emulsion with a modified fatty-acid composition [experimental emulsion (EXP)], or a control enteral diet (ENT) for 22 days. We assayed serum cholestasis markers, measured total bile acid levels in plasma, liver, and gut contents, and analyzed colonic bacterial 16S rRNA gene sequences and metabolomic profiles. Serum cholestasis markers (i.e., bilirubin, bile acids, and γ-glutamyl transferase) were highest in IL-fed pigs and normalized in those given SMOF, EXP, or ENT. Gut bile acid pools were lowest in the IL treatment and were increased in the SMOF and EXP treatments and comparable to ENT. Multiple bile acids, especially their conjugated forms, were higher in the colon contents of SMOF and EXP than in IL pigs. The colonic microbial communities of SMOF and EXP pigs had lower relative abundance of several gram-positive anaerobes, including Clostridrium XIVa, and higher abundance of Enterobacteriaceae than those of IL and ENT pigs. Differences in lipid and microbial-derived compounds were also observed in colon metabolite profiles. These results indicate that multi-component lipid emulsions prevent cholestasis and restore enterohepatic bile flow in association with gut microbial and metabolomic changes. We conclude that sustained bile flow induced by multi-component lipid emulsions likely exerts a dominant effect in reducing bile acid-sensitive gram-positive bacteria.

New generation lipid emulsions increase brain DHA and improve body composition, but not short-term neurodevelopment in parenterally-fed preterm piglets

New generation, multicomponent parenteral lipid emulsions provide key fatty acids for brain growth and development, such as docosahexaenoic acid (DHA) and arachidonic acid (AA), yet the content may be suboptimal for preterm infants. Our aim was to test whether DHA and AA-enriched lipid emulsions would increase activity, growth, and neurodevelopment in preterm piglets and limit brain inflammation. Cesarean-delivered preterm pigs were given three weeks of either enteral preterm infant formula (ENT) or TPN with one of three parenteral lipid emulsions: Intralipid (IL), SMOFlipid (SMOF) or an experimental emulsion (EXP). Activity was continuously monitored and weekly blood sampling and behavioral field testing performed. At termination of the study, whole body and tissue metrics were collected. Neuronal density was assessed in sections of hippocampus (HC), thalamus, and cortex. Frontal cortex (FC) and HC tissue were assayed for fatty acid profiles and expression of genes of neuronal growth and inflammation. After 3 weeks of treatment, brain DHA content in SMOF, EXP and ENT pigs was higher (P < 0.01) in FC but not HC vs. IL pigs. There were no differences in brain weight or neuron density among treatment groups. Inflammatory cytokine TNFα and IL-1β expression in brain regions were increased in IL pigs (P < 0.05) compared to other groups. Overall growth velocity was similar among groups, but IL pigs had higher percent body fat and increased insulin resistance compared to other treatments (P < 0.05). ENT pigs spent more time in higher physical activity levels compared to all TPN groups, but there were no differences in exploratory behavior among groups. We conclude that a soybean oil emulsion increased select brain inflammatory cytokines and multicomponent lipid emulsions enriched with DHA and AA in parenteral lipids results in increased cortical DHA and improved body composition without affecting short term neurodevelopmental outcomes.

Rifampicin, not vitamin E, suppresses parenteral nutrition-associated liver disease development through the pregnane X receptor pathway in piglets

Infants receiving long-term parenteral nutrition (PN) develop PN-associated liver disease (PNALD). We previously (Ng K et al. JPEN J Parenter Enteral Nutr 40: 656-671, 2016. doi:10.1177/0148607114567900.) showed that PN containing soy-based lipid supplemented with vitamin E (α-tocopherol) prevents the development of PNALD. We hypothesize that this occurs via vitamin E activation of pregnane X receptor (PXR)-mediated pathways involved in bile acid metabolism. Neonatal piglets received PN for 14 days containing Intralipid (IL; soy-based lipid emulsion), IL supplemented with 12.6 mg·kg^-1·day^-1 vitamin E (VITE), or IL with 10 mg·kg^-1·day^-1 Rifadin IV (RIF), a PXR agonist. Pigs treated with IL and VITE, but not RIF, developed cholestasis and hyperbilirubinemia, markers of liver disease. The hepatic PXR target genes CYP3A29 and UGT1A6 increased during RIF treatment. RIF also modestly increased metabolism of chenodeoxycholic acid to the more hydrophilic bile acid hyocholic acid. Serum fibroblast growth factor (FGF)-19, a key regulator in suppressing hepatic bile acid synthesis, significantly increased in the RIF group. We conclude rifampicin modified markers of PNALD development by increased metabolism of bile acids and potentially suppressed bile acid synthesis. Vitamin E was ineffective at high lipid doses in preventing PNALD.NEW & NOTEWORTHY Intravenous vitamin E and rifampicin were administered to neonatal piglets receiving parenteral nutrition to determine their efficacy in reducing the progression of parenteral nutrition-associated liver disease (PNALD). Rifampicin increased serum FGF-19 concentrations and synthesis of the bile acid hyocholic acid which led to a reduction of PNALD parameters at 2 wk of administration. This result has potential clinical implications for the use of rifampicin as a safe and inexpensive treatment for short-term development of PNALD.

Metabolomic Characterization of a Novel Pig Model of Pediatric Non-alcoholic Fatty Liver Disease (P08-131-19)

Objectives

Non-alcoholic fatty liver disease (NAFLD) is a leading nutrition-linked liver disease in children. We have recently identified the neonatal Iberian pig as a novel model of pediatric NAFLD. Interestingly, feeding a high fructose-high fat (HFF) diet to neonatal Iberian pigs for 10 weeks did not induce obesity and decreased high and low density lipoproteins in serum, while the liver exhibited many of the histological features of pediatric NAFLD. In this study we utilized a metabolomics approach to characterize the metabolic phenotype of this pig model.

Methods

Plasma and liver samples collected from Iberian pigs fed control, HFF, control + probiotic and HFF + probiotic diets were analyzed by LC-MS using targeted assays for primary metabolomics, aminomics, and lipidomics. Data was analyzed with multivariate statistics and 2-way ANOVA with t-tests adjusted for false discovery rate.

Results

Results from multivariate tests indicated no diet × probiotic interaction or probiotic effect, so only the main effect of diet is shown. A total of 224 and 218 metabolites were identified in the plasma and liver, respectively. In agreement with previous NAFLD models, the HFF diet increased hepatic branched chain amino acids, cholesteryl esters, hydroxyproline, plasma acylcarnitines and primary bile acids, and altered hepatic triacylglycerol-species composition (P < 0.0001). In addition, HFF pigs had increased homocysteine and methionine levels combined with a decrease in pyridoxate in liver (P < 0.0001), suggesting a disruption in the one carbon cycle and its methyl donation capability. HFF decreased hepatic choline and betaine (P < 0.0001), which may indicate a compensatory use of the methyl groups of these compounds. The aforementioned reduction of choline used for the CDP-choline pathway and the potential one carbon cycle impact on SAM availability for the phosphatidylethanolamine N-methyltransferase (PEMT) pathway may explain the observed differential changes in hepatic phosphatidylcholines (P < 0.0001), which are required for the production of very low density lipoproteins (VLDL).

Conclusions

Unique features of this model such as reduced plasma lipoproteins and lack of weight gain in the presence of hepatic steatosis may be related to an altered one carbon cycle impacting phosphatidylcholine production.

Funding Sources

ARI, AcornSeekers.

Continuous Feeding Does Not Blunt Skeletal Muscle Protein Synthesis and Lean Growth Compared to Intermittent Bolus Feeding in the Preterm Piglet (OR26-06-19)

Objectives

Refining early feeding strategies for premature infants is essential for mitigating adverse outcomes of prematurity. In neonatal term piglets, continuous feeding blunts growth compared to intermittent bolus feeding. Our objective was to determine the impact of feeding modality on lean growth in preterm pigs. We hypothesized that intermittent bolus feeding can mitigate low lean growth rates in preterm neonates compared to continuous feeding.

Methods

Pigs obtained by C-section (105 d gestation; 952 ± 205 g body weight) were fitted with an umbilical artery catheter (later replaced with jugular vein catheter) and an orogastric tube for parenteral and enteral nutrition, respectively. Pigs were assigned to continuous (CONT; 7.5 mL/[kg·h]) or intermittent bolus (INT; 30 mL/kg every 4 h over 15 min) feeding for 21 d. Pigs initially received parenteral nutrition and were advanced to full oral feeds over 6 d (220 kcal/kg and 16 g/kg protein per day). Body composition (by DXA), plasma insulin, and skeletal muscle anabolic signaling and fractional protein synthesis rates (PS; L-[ring-2H5]phenylalanine) were determined in INT pigs in the postabsorptive (before a meal, INT-PA; n = 13) and postprandial (after a meal, INT-PP; n = 16) states and in CONT pigs (n = 14).

Results

Body weight gain, lean mass, and fat mass did not differ between INT and CONT pigs. Insulin was lower before feeding for INT pigs than CONT pigs (P < 0.05). Insulin increased with feeding for INT pigs and exceeded that of CONT pigs at 30 and 60 min (P < 0.01) before returning to baseline levels at 240 min. In the longissimus dorsi (LD), gastrocnemius, and soleus muscles, the abundance of the eIF4E·eIF4G complex, which is required for translation initiation, was greater in INT-PP and CONT pigs than INT-PA pigs (P < 0.01), but did not differ between INT-PP and CONT pigs. PS in the LD muscle was greater in INT-PP pigs than INT-PA pigs (P < 0.01), but did not differ between INT-PP and CONT pigs.

Conclusions

Continuous feeding does not blunt translation initiation and protein synthesis in skeletal muscle compared to intermittent bolus feeding in preterm piglets. The resulting absence of enhanced lean growth with intermittent bolus compared to continuous feeding contrasts with term piglets and may be a consequence of prematurity.

Funding Sources

USDA CRIS 6250-51000-055, NIH HD072891, and USDA NIFA 2013-67015-20438.

A Diet-Induced Pediatric Model of Non Alcoholic Fatty Liver Disease Using Neonatal Iberian Pigs (OR26-02-19)

Objectives

The prevalence of non-alcoholic fatty liver disease (NAFLD) in children has increased over the past decades, creating a need for animal models that recapitulate the features of the pediatric disease. Iberian pigs have a leptin-resistant phenotype characterized by hyperleptinemia, hyperphagia, and extreme adipogenesis. We hypothesized that neonatal Iberian pigs fed a high-fat high-fructose (HFF) diet will develop a pattern of liver injury resembling pediatric NAFLD. In addition, we sought to determine if a mixture of probiotics would prevent the disease.

Methods

Animals were fed 1 of 4 diets containing (g/kg body weight × d) 0 g fructose, 11 g fat and 199 kcal (CON-N; n = 8), 22 g fructose, 16 g fat and 300 kcal (HFF-N; n = 6), CON + probiotic (CON-P; n = 6), or HFF + probiotic (HFF-P; n = 6) every 6 h for 70 d. The probiotic mixture (6.2 × 104cfu/mL) contained Pediococcus, Lactobacillus and Bacillus. Body weight was recorded every 3 d. Serum markers of liver injury and dyslipidemia were measured on d 65 at 2 h post feeding. Fasting leptin, insulin, glucose and homeostatic model assessment (HOMA) values were assessed on d 70. Liver tissue was collected on d 70 for histology, triacylglyceride (TG) quantification, and gene expression of tumor necrosis factor (TNF) α, tumor growth factor (TGF) β, interleukin (IL) 1α, peroxisome proliferator-activated receptor (PPAR) γ, carbohydrate-responsive element-binding protein (ChREBP) and sterol regulatory element-binding protein (SREBP) 1c.

Results

Body weight was higher in CON-P, and insulin and HOMA values in HFF-P and CON-P (P ≤ 0.05). Leptin, alanine and aspartate aminotransferases, alkaline phosphatase, lactate dehydrogenase and total bilirubin were increased (P ≤ 0.001), and high and low density lipoproteins decreased (P ≤ 0.05) in HFF-N and HFF-P. Livers in HFF-P and HFF-N had higher relative weight and TG (P ≤ 0.001), micro and macrovesicular steatosis, ballooning degeneration, Mallory-denk bodies, inflammation and necrosis, increased gene expression of TNFα, TGFβ, IL1α and PPARγ (P ≤ 0.001), and decreased ChREBP (P ≤ 0.001).

Conclusions

Iberian pigs fed a HFF diet recapitulate many pediatric NAFLD-associated features, in the absence of obesity and independently of probiotic supplementation, suggesting a potentially suitable model for pediatric NAFLD research.

Funding Sources

ARI, AcornSeekers.

Western Diet-Induced Dysbiosis Is Associated with Intestinal Hyperplasia and Dysregulation of FXR-FGF19 Gene Expression in Juvenile Iberian Pigs (OR26-03-19)

Objectives

The Western diet has been associated with increased risk of colon cancer, partially due to changes in bile acid (BA) homeostasis. While diet-induced proliferation of intestinal mucosa has been documented in adults, it is unclear whether it can develop in pediatric populations. We hypothesize that feeding a high-fat high-fructose (HFF) diet to neonatal pigs will increase BA levels in liver and plasma, and cell proliferation in intestinal mucosa. In addition, we hypothesize that supplementation of a probiotic mixture with Pediococcus, Lactobacillus and Bacillus at 6.2 × 104 cfu/mL will ameliorate the HFF pro-proliferative effect.

Methods

To test the hypothesis we used 10-d old Iberian pigs, which have a leptin-resistant phenotype resulting in rapid development of obesity and dyslipidemia. Diets contained (g/kg body weight × d) 0 g fructose, 11 g fat and 199 kcal (CON-N; n = 8), 22 g fructose, 16 g fat and 300 kcal (HFF-N; n = 6), CON + probiotic (CON-P; n = 6), or HFF + probiotic (HFF-P; n = 6). Pigs were euthanized at 80 d of age. Liver and plasma BA levels were analyzed by LC-MS. Hyperplasia in colon and distal ileum (DI) was assessed by hematoxylin-eosin and Ki-67 staining. Bacteria in colon content were quantified at genus level by 16S ribosomal RNA analysis. Gene expression of farnesoid X receptor (FXR), small heterodimer partner (SHP), fibroblast growth factor 19 (FGF19), organic solute transporter (OST) α, apical sodium-dependent BA transporter (ASBT), tumor necrosis factor (TNF) α, tumor growth factor (TGF) β, takeda G-protein receptor (TGR) 5, and epidermal growth factor receptor (EGFR) was measured by qPCR.

Results

HFF-N an HFF-P increased taurocholate and glyocholate in liver and plasma (P ≤ 0.0001), crypt depth, villi length and Ki-67 + cells/crypt (P ≤ 0.01) in colon and DI, and Clostridium, Bacteroides, Synergistes, and Bilophila populations in colon content (P ≤ 0.05). HFF-N and HFF-P increased expression of SHP, OSTα, and ASBT and decreased FGF19 in DI (P ≤ 0.05), and increased SHP and decreased TNFα and TGFβ in colon (P ≤ 0.05). FXR, TGR5 and EGFR did not differ between groups.

Conclusions

A high-fructose high-fat diet increased liver and plasma BA levels and downregulated FGF19 expression in DI. Colonic hyperplasia, proliferation of BA tolerant bacteria and changes in SHP, TNFα and TGFβ may be related to increased secondary BA in the colon.

Funding Sources

ARI, AcornSeekers, STRIDE.

Reduced Plasma Amino Acid Levels During Allogeneic Hematopoietic Stem Cell Transplantation Are Associated with Systemic Inflammation and Treatment-Related Complications

Patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) are challenged by cytotoxic effects of the conditioning regimen, resulting in tissue damage, systemic inflammation, and increased metabolic demands for amino acids to regenerate damaged tissues, reconstitute hematopoietic cells, and establish antioxidant defenses. To date, few studies have addressed the role of plasma amino acid (PAA) levels during transplantation, and it remains unknown if amino acid deficiency can aggravate treatment-related morbidity. We determined plasma levels of the 23 human amino acids in 80 HSCT recipients (age 1.1 to 55.4 years) before conditioning and on days +7 and +21 post-transplant along with C-reactive protein (CRP) and IL-6 levels on day +7. Significant changes were observed in plasma concentrations of several human amino acids during HSCT. On day +7, numerous amino acids were inversely correlated with both CRP and IL-6, including glutamic acid, serine, alanine, glutamine, arginine, cysteine, glycine, histidine, lysine, tryptophan, threonine, taurine, proline, and methionine (r = -.22 to -.66; all P < .05). Patients who developed sinusoidal obstruction syndrome (SOS) had significantly lower mean total PAA levels compared with patients without SOS (2013 ng/L [95% confidence interval (CI), 1709 to 2318 ng/L] versus 2706 ng/L [95% CI, 2261 to 3150 ng/L]; P = .006), along with lower individual levels of glutamic acid, serine, arginine, glycine, lysine, valine, tryptophan, threonine, and proline on day +7 (all P < .05). Patients with severe acute graft-versus-host disease had a lower mean total PAA level (1922 ng/L [95% CI, 1738 to 2106 ng/L] versus 2649 ng/L [95% CI, 2244 to 3055 ng/L]; P = .014) and lower levels of serine, glutamine, cysteine, glycine, lysine, and threonine on day +7 (all P < .05). These results indicate a relationship between low concentrations of certain amino acids and the risk of treatment-related complications.

Metabolomic signatures distinguish the impact of formula carbohydrates on disease outcome in a preterm piglet model of NEC

BACKGROUND

Major risk factors for necrotizing enterocolitis (NEC) include premature birth and formula feeding in the context of microbial colonization of the gastrointestinal tract. We previously showed that feeding formula composed of lactose vs. corn syrup solids protects against NEC in preterm pigs; however, the microbial and metabolic effects of these different carbohydrates used in infant formula has not been explored.

OBJECTIVE

Our objective was to characterize the effects of lactose- and corn syrup solid-based formulas on the metabolic and microbial profiles of preterm piglets and to determine whether unique metabolomic or microbiome signatures correlate with severity or incidence of NEC.

DESIGN/METHODS

Preterm piglets (103 days gestation) were given total parenteral nutrition (2 days) followed by gradual (5 days) advancement of enteral feeding of formulas matched in nutrient content but containing either lactose (LAC), corn syrup solids (CSS), or 1:1 mix (MIX). Gut contents and mucosal samples were collected and analyzed for microbial profiles by sequencing the V4 region of the 16S rRNA gene. Metabolomic profiles of cecal contents and plasma were analyzed by LC/GC mass spectrometry.

RESULTS

NEC incidence was 14, 50, and 44% in the LAC, MIX, and CSS groups, respectively. The dominant classes of bacteria were Bacilli, Clostridia, and Gammaproteobacteria. The number of observed OTUs was lowest in colon contents of CSS-fed pigs. CSS-based formula was associated with higher Bacilli and lower Clostridium from clusters XIVa and XI in the colon. NEC was associated with decreased Gammaproteobacteria in the stomach and increased Clostridium sensu stricto in the ileum. Plasma from NEC piglets was enriched with metabolites of purine metabolism, aromatic amino acid metabolism, and bile acids. Markers of glycolysis, e.g., lactate, were increased in the cecal contents of CSS-fed pigs and in plasma of pigs which developed NEC.

CONCLUSIONS

Feeding formula containing lactose is not completely protective against NEC, yet selects for greater microbial richness associated with changes in Bacilli and Clostridium and lower NEC incidence. We conclude that feeding preterm piglets a corn syrup solid vs. lactose-based formula increases the incidence of NEC and produces distinct metabolomic signatures despite modest changes in microbiome profiles.

Acute activation of GLP-1-expressing neurons promotes glucose homeostasis and insulin sensitivity

OBJECTIVE

Glucagon-like peptides are co-released from enteroendocrine L cells in the gut and preproglucagon (PPG) neurons in the brainstem. PPG-derived GLP-1/2 are probably key neuroendocrine signals for the control of energy balance and glucose homeostasis. The objective of this study was to determine whether activation of PPG neurons per se modulates glucose homeostasis and insulin sensitivity in vivo.

METHODS

We generated glucagon (Gcg) promoter-driven Cre transgenic mice and injected excitatory hM3Dq-mCherry AAV into their brainstem NTS. We characterized the metabolic impact of PPG neuron activation on glucose homeostasis and insulin sensitivity using stable isotopic tracers coupled with hyperinsulinemic euglycemic clamp.

RESULTS

We showed that after ip injection of clozapine N-oxide, Gcg-Cre lean mice transduced with hM3Dq in the brainstem NTS downregulated basal endogenous glucose production and enhanced glucose tolerance following ip glucose tolerance test. Moreover, acute activation of PPG neurons^NTS enhanced whole-body insulin sensitivity as indicated by increased glucose infusion rate as well as augmented insulin-suppression of endogenous glucose production and gluconeogenesis. In contrast, insulin-stimulation of glucose disposal was not altered significantly.

CONCLUSIONS

We conclude that acute activation of PPG neurons in the brainstem reduces basal glucose production, enhances intraperitoneal glucose tolerance, and augments hepatic insulin sensitivity, suggesting an important physiological role of PPG neurons-mediated circuitry in promoting glycemic control and insulin sensitivity.

Replication of human noroviruses in stem cell-derived human enteroids

The major barrier to research and development of effective interventions for human noroviruses (HuNoVs) has been the lack of a robust and reproducible in vitro cultivation system. HuNoVs are the leading cause of gastroenteritis worldwide. We report the successful cultivation of multiple HuNoV strains in enterocytes in stem cell-derived, nontransformed human intestinal enteroid monolayer cultures. Bile, a critical factor of the intestinal milieu, is required for strain-dependent HuNoV replication. Lack of appropriate histoblood group antigen expression in intestinal cells restricts virus replication, and infectivity is abrogated by inactivation (e.g., irradiation, heating) and serum neutralization. This culture system recapitulates the human intestinal epithelium, permits human host-pathogen studies of previously noncultivatable pathogens, and allows the assessment of methods to prevent and treat HuNoV infections.

Multi-omic profiles of hepatic metabolism in TPN-fed preterm pigs administered new generation lipid emulsions

We aimed to characterize the lipidomic, metabolomic, and transcriptomic profiles in preterm piglets administered enteral (ENT) formula or three parenteral lipid emulsions [parenteral nutrition (PN)], Intralipid (IL), Omegaven (OV), or SMOFlipid (SL), for 14 days. Piglets in all parenteral lipid groups showed differential organ growth versus ENT piglets; whole body growth rate was lowest in IL piglets, yet there were no differences in either energy expenditure or (13)C-palmitate oxidation. Plasma homeostatic model assessment of insulin resistance demonstrated insulin resistance in IL, but not OV or SL, compared with ENT. The fatty acid and acyl-CoA content of the liver, muscle, brain, and plasma fatty acids reflected the composition of the dietary lipids administered. Free carnitine and acylcarnitine (ACT) levels were markedly reduced in the PN groups compared with ENT piglets. Genes associated with oxidative stress and inflammation were increased, whereas those associated with alternative pathways of fatty acid oxidation were decreased in all PN groups. Our results show that new generation lipid emulsions directly enrich tissue fatty acids, especially in the brain, and lead to improved growth and insulin sensitivity compared with a soybean lipid emulsion. In all total PN groups, carnitine levels are limiting to the formation of ACTs and gene expression reflects the stress of excess lipid on liver function.

Animal models of gastrointestinal and liver diseases. Animal models of infant short bowel syndrome: translational relevance and challenges

Intestinal failure (IF), due to short bowel syndrome (SBS), results from surgical resection of a major portion of the intestine, leading to reduced nutrient absorption and need for parenteral nutrition (PN). The incidence is highest in infants and relates to preterm birth, necrotizing enterocolitis, atresia, gastroschisis, volvulus, and aganglionosis. Patient outcomes have improved, but there is a need to develop new therapies for SBS and to understand intestinal adaptation after different diseases, resection types, and nutritional and pharmacological interventions. Animal studies are needed to carefully evaluate the cellular mechanisms, safety, and translational relevance of new procedures. Distal intestinal resection, without a functioning colon, results in the most severe complications and adaptation may depend on the age at resection (preterm, term, young, adult). Clinically relevant therapies have recently been suggested from studies in preterm and term PN-dependent SBS piglets, with or without a functional colon. Studies in rats and mice have specifically addressed the fundamental physiological processes underlying adaptation at the cellular level, such as regulation of mucosal proliferation, apoptosis, transport, and digestive enzyme expression, and easily allow exogenous or genetic manipulation of growth factors and their receptors (e.g., glucagon-like peptide 2, growth hormone, insulin-like growth factor 1, epidermal growth factor, keratinocyte growth factor). The greater size of rats, and especially young pigs, is an advantage for testing surgical procedures and nutritional interventions (e.g., PN, milk diets, long-/short-chain lipids, pre- and probiotics). Conversely, newborn pigs (preterm or term) and weanling rats provide better insights into the developmental aspects of treatment for SBS in infants owing to their immature intestines. The review shows that a balance among practical, economical, experimental, and ethical constraints will determine the choice of SBS model for each clinical or basic research question.

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.

Modulation of the gut microbiota with antibiotic treatment suppresses whole body urea production in neonatal pigs

We examined whether changes in the gut microbiota induced by clinically relevant interventions would impact the bioavailability of dietary amino acids in neonates. We tested the hypothesis that modulation of the gut microbiota in neonatal pigs receiving no treatment (control), intravenously administered antibiotics, or probiotics affects whole body nitrogen and amino acid turnover. We quantified whole body urea kinetics, threonine fluxes, and threonine disposal into protein, oxidation, and tissue protein synthesis with stable isotope techniques. Compared with controls, antibiotics reduced the number and diversity of bacterial species in the distal small intestine (SI) and colon. Antibiotics decreased plasma urea concentrations via decreased urea synthesis. Antibiotics elevated threonine plasma concentrations and turnover, as well as whole body protein synthesis and proteolysis. Antibiotics decreased protein synthesis rate in the proximal SI and liver but did not affect the distal SI, colon, or muscle. Probiotics induced a bifidogenic microbiota and decreased plasma urea concentrations but did not affect whole body threonine or protein metabolism. Probiotics decreased protein synthesis in the proximal SI but not in other tissues. In conclusion, modulation of the gut microbiota by antibiotics and probiotics reduced hepatic ureagenesis and intestinal protein synthesis, but neither altered whole body net threonine balance. These findings suggest that changes in amino acid and nitrogen metabolism resulting from antibiotic- or probiotic-induced shifts in the microbiota are localized to the gut and liver and have limited impact on whole body growth and anabolism in neonatal piglets.

Ontogeny of methionine utilization and splanchnic uptake in critically ill children

To determine the rates of methionine splanchnic uptake and utilization in critically ill pediatric patients we used two kinetic models: the plasma methionine enrichment and the "intracellular" homocysteine enrichment. Twenty four patients, eight infants, eight children, and eight adolescents, were studied. They received simultaneous, primed, constant, intravenous infusions of l-[(2)H(3)]methylmethionine and enteral l-[1-(13)C]methionine. The ratio of [(13)C]homocysteine to [(13)C]methionine enrichment was 1.0 ± 0.15, 0.80 ± 0.20, and 0.66 ± 0.10, respectively, for the infants, children, and adolescents, and it was different between the infants and adolescents (P < 0.01). Methionine splanchnic uptake was 63, 45, and 36%, respectively, in the infants, children, and adolescents, and it was higher (P < 0.01) in the infants compared with the adolescents. The infants utilized 73% of methionine flux for nonoxidative disposal, while 27% was used for transulfuration (P < 0.001). Conversely, in the adolescents, 40% was utilized for nonoxidative disposal, while 60% was used for transulfuration. There is ontogeny on the rates of methionine splanchnic uptake and on the fate of methionine utilization in critically ill children, with greater methionine utilization for synthesis of proteins and methionine-derived compounds (P < 0.01) and decreased transulfuration rates in the infants (P < 0.01), while the opposite was observed in the adolescents. The plasma model underestimated methionine kinetics in children and adolescents but not in the infants, suggesting lesser dilution and greater compartmentation of methionine metabolism in the infant population. All patients were in negative methionine balance, indicating that the current enteral nutritional support is inadequate in these patients.

Glucagon-like peptide 2: a key link between nutrition and intestinal adaptation in neonates?

This paper reviews the evidence from recent studies in young piglets to examine the hypothesis that glucagon-like peptide 2 (GLP-2) is a physiologically relevant hormonal signal linked to the intestinal adaptation associated with enteral nutrition in neonates. Observations that support the hypothesis include, 1) the GLP-2 secretory response to enteral nutrition is functional as early as late gestation, 2) parallel changes in intestinal growth and circulating GLP-2 occur in response to the quantity and composition of enteral nutrition after birth, and 3) the acute temporal changes in intestinal metabolism and circulating GLP-2 concentrations in response to enteral nutrition are generally coincident. In contrast, however, the lack of intestinal trophic responses to both pharmacological GLP-2 concentrations in the fetus and weanling pigs, and to physiological GLP-2 concentrations in neonates raises doubts concerning the physiological relevance of GLP-2 as a enterally mediated trophic signal. A more definitive test of this hypothesis will require further studies that assess the intestinal metabolic response to enteral nutrition using experimental approaches that block GLP-2 action.

Total parenteral nutrition adversely affects gut barrier function in neonatal piglets

Sepsis is the most common morbidity in preterm infants, who often receive total parenteral nutrition (TPN). We hypothesized that gut barrier function is compromised in TPN-fed compared with enterally fed newborn piglets (ENT pigs). Colostrum-deprived newborn pigs were implanted with jugular venous and bladder catheters under general anesthesia. Pigs were either administered TPN (n = 15) or fed formula (ENT pigs, n = 15). After 6 days, pigs were gavaged a solution of mannitol, lactulose, and polyethylene glycol 4000 (PEG 4000) and urine was collected for 24 h. At 7 days, small bowel samples were assayed for myeloperoxidase activity, morphometry, and tight junction protein abundance. Intestinal contents and peripheral organ sites were cultured for bacteria. Urinary recovery (%dose) of mannitol (53 vs. 68) was lower, whereas that of lactulose (2.93 vs. 0.18) and PEG 4000 (12.78 vs. 0.96) were higher in TPN vs. ENT pigs, respectively (P < 0.05). Incidence of translocation was similar in TPN and ENT pigs. Myeloperoxidase activity was increased in TPN vs. ENT pigs in the jejunum (P < 0.001) and was weakly correlated with lactulose (R2 = 0.32) and PEG 4000 (R2 = 0.38) recovery. Goblet cell counts did not change, but intraepithelial lymphocyte numbers decreased with TPN. Only claudin-1 protein abundance was increased in the TPN group. We conclude that TPN is associated with impairment of neonatal gut barrier function as measured by permeability but not translocation.

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.