Postprandial intestinal and whole body nitrogen kinetics and distribution in piglets fed a single meal

Differential effects of milk proteins on amino acid digestibility, post-prandial nitrogen utilization and intestinal peptide profiles in rats

OBJECTIVE

The aim of this study was to analyze the protein digestibility and postprandial metabolism in rats of milk protein matrices obtained by different industrial processes.

MATERIAL AND METHODS

The study was conducted on Wistar rats that consumed a meal containing different ¹⁵N-labeled milk proteins. Four milk matrices were tested: native micellar caseins (C1), caseins low in calcium (C2 low Ca²⁺), a matrix containing a ratio 63:37 of caseins and whey proteins (CW2) and whey proteins alone (W). Blood and urine were collected during the postprandial period and rats were euthanized 6 h after meal intake to collect digestive contents and organs.

RESULTS

Orocaecal digestibility values of amino acids ranged between 96.0 ± 0.2% and 96.6 ± 0.4% for C1-, C2 low Ca²⁺- and W-matrices, while this value was significantly lower for CW2 matrix (92.4 ± 0.5%). More dietary nitrogen was sequestered in the splanchnic area (intestinal mucosa and liver) as well as in plasma proteins after ingestion of W matrix, especially compared to the C1- and C2 low Ca²⁺-matrices. Peptidomic analysis showed that more milk protein-derived peptides were identified in the caecum of rats after the ingestion of the matrices containing caseins compared to W matrix.

CONCLUSION

We found that demineralization of micellar caseins did not modify its digestibility and postprandial metabolism. The low digestibility of the modified casein-to-whey ratio matrix may be ascribed to a lower accessibility of the protein to digestive enzymes due to changes in the protein structure, while the higher nitrogen splanchnic retention after ingestion of whey was probably due to the fast assimilation of its protein content. Finally, our results showed that industrial processes that modify the structure and/or composition of milk proteins influence protein digestion and utilization.

Antioxidant potential of Pediococcus pentosaceus strains from the sow milk bacterial collection in weaned piglets

BACKGROUND

In modern animal husbandry, breeders pay increasing attention to improving sow nutrition during pregnancy and lactation to favor the health of neonates. Sow milk is a main food source for piglets during their first three weeks of life, which is not only a rich repository of essential nutrients and a broad range of bioactive compounds, but also an indispensable source of commensal bacteria. Maternal milk microorganisms are important sources of commensal bacteria for the neonatal gut. Bacteria from maternal milk may confer a health benefit on the host.

METHODS

Sow milk bacteria were isolated using culturomics followed by identification using 16S rRNA gene sequencing. To screen isolates for potential probiotic activity, the functional evaluation was conducted to assess their antagonistic activity against pathogens in vitro and evaluate their resistance against oxidative stress in damaged Drosophila induced by paraquat. In a piglet feeding trial, a total of 54 newborn suckling piglets were chosen from nine sows and randomly assigned to three treatments with different concentrations of a candidate strain. Multiple approaches were carried out to verify its antioxidant function including western blotting, enzyme activity analysis, metabolomics and 16S rRNA gene amplicon sequencing.

RESULTS

The 1240 isolates were screened out from the sow milk microbiota and grouped into 271 bacterial taxa based on a nonredundant set of 16S rRNA gene sequencing. Among 80 Pediococcus isolates, a new Pediococcus pentosaceus strain (SMM914) showed the best performance in inhibition ability against swine pathogens and in a Drosophila model challenged by paraquat. Pretreatment of piglets with SMM914 induced the Nrf2-Keap1 antioxidant signaling pathway and greatly affected the pathways of amino acid metabolism and lipid metabolism in plasma. In the colon, the relative abundance of Lactobacillus was significantly increased in the high dose SMM914 group compared with the control group.

CONCLUSION

P. pentosaceus SMM914 is a promising probiotic conferring antioxidant capacity by activating the Nrf2-Keap1 antioxidant signaling pathway in piglets. Our study provided useful resources for better understanding the relationships between the maternal microbiota and offspring. Video Abstract.

Moderate adiposity levels counteract protein metabolism modifications associated with aging in rats

PURPOSE

Physiological parameters such as adiposity and age are likely to influence protein digestion and utilization. The aim of this study was to evaluate the combined effects of age and adiposity on casein protein and amino acid true digestibility and its postprandial utilization in rats.

METHODS

Four groups were included (n = 7/8): 2 months/normal adiposity, 2 months/high adiposity, 11 months/normal adiposity and 11 months/high adiposity. Rats were given a calibrated meal containing ¹⁵N-labeled casein (Ingredia, Arras, France) and were euthanized 6 h later. Digestive contents were collected to assess protein and amino acid digestibilities. ¹⁵N enrichments were measured in plasma and urine to determine total body deamination. Fractional protein synthesis rate (FSR) was determined in different organs using a flooding dose of ¹³C valine.

RESULTS

Nitrogen and amino acid true digestibility of casein was around 95-96% depending on the group and was increased by 1% in high adiposity rats (P = 0.04). Higher adiposity levels counteracted the increase in total body deamination (P = 0.03) that was associated with older age. Significant effects of age (P = 0.006) and adiposity (P = 0.002) were observed in the muscle FSR, with age decreasing it and adiposity increasing it.

CONCLUSION

This study revealed that a higher level of adiposity resulted in a slight increase in protein and individual amino acid true digestibility values and seemed to compensate for the metabolic postprandial protein alterations observed at older age.

Effects of supplementation of graded level of glutamic acid to crude protein reduced diets on the performance of growing pigs

A total of 150 growing pigs ([Landrace × Yorkshire] × Duroc) with an initial average body weight (BW) of 24.45 kg were used in a 6-week trial to estimate the optimum lysine to glutamic acid ratio in pigs fed low-protein diets supplemented with increasing level of synthetic glutamic acid (Glu). Pigs were randomly allotted to 5 dietary treatments consisting of either control diet (CON) formulated to have 157 g crude protein (CP) or negative control diets (NC, NC1, NC2 and NC3) with 20 g CP reduction and addition of Glu (1.1, 3.9, 6.8 and 9.6 g/kg feed respectively). Supplementing the increasing level of Glu to low CP diets did not exert any linear or quadratic responses in the growth performance parameters as well as nutrient digestibility. The serum creatinine concentration in pigs receiving CON diet showed trends (p = 0.063) in increment compared with pigs receiving NC diet. However, with the increase in the supplementation of Glu, there were no linear or quadratic responses on serum blood urea nitrogen (BUN) and creatinine concentrations. There was a tendency in the reduction (p = 0.088, p = 0.064) of backfat thickness and lean percentage, respectively, at week 3 and a trend in the reduction (p = 0.092) in lean percentage at week 6 in pigs fed NC diet compared with those fed CON diet. The increase in the supplemental level of Glu tended to show quadratic responses in the backfat thickness and lean percentage at week 3 and 6. In conclusion, the growth performance parameters as well as carcass traits with Lys: Glu ratio 1: 2.71 were very close with the mean values of CON diet indicating that 6.8 g Glu when supplemented to 2% CP reduced diet could achieve the comparable growth performance and carcass trait as that of standard basal diet.

Intermittent Bolus Feeding Enhances Organ Growth More Than Continuous Feeding in a Neonatal Piglet Model

BACKGROUND

Orogastric tube feeding is frequently prescribed for neonates who cannot ingest food normally. In a piglet model of the neonate, greater skeletal muscle growth is sustained by upregulation of translation initiation signaling when nutrition is delivered by intermittent bolus meals, rather than continuously.

OBJECTIVES

The objective of this study was to determine the long-term effects of feeding frequency on organ growth and the mechanism by which feeding frequency modulates protein anabolism in these organs.

METHODS

Eighteen neonatal pigs were fed by gastrostomy tube the same amount of a sow milk replacer either by continuous infusion (CON) or on an intermittent bolus schedule (INT). After 21 d of feeding, the pigs were killed without interruption of feeding (CON; n = 6) or immediately before (INT-0; n = 6) or 60 min after (INT-60; n = 6) a meal, and fractional protein synthesis rates and activation indexes of signaling pathways that regulate translation initiation were measured in the heart, jejunum, ileum, kidneys, and liver.

RESULTS

Compared with continuous feeding, intermittent feeding stimulated the growth of the liver (+64%), jejunum (+48%), ileum (+40%), heart (+64%), and kidney (+56%). The increases in heart, kidney, jejunum, and ileum masses were proportional to whole body lean weight gain, but liver weight gain was greater in the INT-60 than the CON, and intermediate for the INT-0 group. For the liver and ileum, but not the heart, kidney, and jejunum, INT-60 compared with CON pigs had greater fractional protein synthesis rates (22% and 48%, respectively) and was accompanied by an increase in ribosomal protein S6 kinase 1 and eukaryotic initiation factor 4E binding protein 1 phosphorylation.

CONCLUSIONS

These results suggest that intermittent bolus compared with continuous orogastric feeding enhances organ growth and that in the ileum and liver, intermittent feeding enhances protein synthesis by stimulating translation initiation.

Activation of Pyruvate Dehydrogenase by Sodium Dichloroacetate Shifts Metabolic Consumption from Amino Acids to Glucose in IPEC-J2 Cells and Intestinal Bacteria in Pigs

The extensive metabolism of amino acids (AA) as fuel is an important reason for the low use efficiency of protein in pigs. In this study, we investigated whether regulation of the pyruvate dehydrogenase kinase (PDK)/pyruvate dehydrogenase alpha 1 (PDHA1) pathway affected AA consumption by porcine intestinal epithelial (IPEC-J2) cells and intestinal bacteria in pigs. The effects of knockdown of PDHA1 and PDK1 with small interfering RNA (siRNA) on nutrient consumption by IPEC-J2 cells were evaluated. IPEC-J2 cells were then cultured with sodium dichloroacetate (DCA) to quantify AA and glucose consumption and nutrient oxidative metabolism. The results showed that knockdown of PDHA1 using siRNA decreased glucose consumption but increased total AA (TAA) and glutamate (Glu) consumption by IPEC-J2 cells ( P < 0.05). Opposite effects were observed using siRNA targeting PDK1 ( P < 0.05). Additionally, culturing IPEC-J2 cells in the presence of 5 mM DCA markedly increased the phosphorylation of PDHA1 and PDH phosphatase 1, but inhibited PDK1 phosphorylation ( P < 0.05). DCA treatment also reduced TAA and Glu consumption and increased glucose depletion ( P < 0.05). These results indicated that PDH was the regulatory target for shifting from AA metabolism to glucose metabolism and that culturing cells with DCA decreased the consumption of AAs by increasing the depletion of glucose through PDH activation.

L-Glutamate Enhances Barrier and Antioxidative Functions in Intestinal Porcine Epithelial Cells

BACKGROUND

L-Glutamate (Glu) is a major amino acid in milk and postweaning diets for mammals (including pigs and human infants). However, effects of Glu on intestinal mucosal barrier and antioxidative functions are unknown.

OBJECTIVE

This study tested the hypothesis that Glu may enhance the barrier function of intestinal porcine epithelial cell line 1 (IPEC-1) cells by upregulating the expression of tight junction proteins.

METHODS

IPEC-1 cells were cultured with or without Glu in the presence or absence of 1 mmol/L diquat (an oxidant) for indicated time points. Cell numbers, transepithelial electrical resistance (TEER), mRNA, and protein abundance of glutamate transporter, the release of lactate dehydrogenase (LDH), and the abundance of tight junction proteins were determined.

RESULTS

Compared with 0 mmol/L Glu, 0.5-, 1-, and 2 mmol/L Glu stimulated (P < 0.05) cell growth by 13-37% at 24 h and 12-34% at 48 h, respectively. In addition, 0.5 mmol/L Glu increased (P < 0.05) TEER (by 58% at 24 h and by 98% at 48 h, respectively). These effects of Glu were associated with increased mRNA abundance of Glu transporter solute carrier family 1 member 1 (SLC1A1) by 30-130% and protein abundance of excitatory amino acid transporter 3 (encoded by SLC1A1) by 19-34%, respectively. In a cell model of oxidative stress induced by 1 mmol/L diquat, 0.5 mmol/L Glu enhanced cell viability, TEER, and membrane integrity (as indicated by the reduced release of LDH) in IPEC-1 cells by increasing the abundance of the tight junction proteins occludin, claudin-3, zonula occludens (ZO)-2, and ZO-3.

CONCLUSION

These findings indicate that Glu plays an important role in mucosal barrier function by enhancing cell growth and maintaining membrane integrity in response to oxidative stress.

Evidence for a role of the ileum in the control of nitrogen homeostasis via the regulation of arginine metabolism

As arginine plays a key role in the regulation of liver ureagenesis, we hypothesised that a modulation of enzymes involved in arginine metabolism within the intestine contributes to the regulation of N homeostasis according to protein supply. Our aim was to study the influence of variations in protein or amino acid (AA) supply on intestinal arginase, glutaminase, ornithine aminotransferase (OAT), argininosuccinate lyase and argininosuccinate synthetase. We evaluated in vivo in rats the responses of these enzymes to short-term (ST, 16 h) and long-term (LT, 15 d) variations in dietary protein (10, 17 or 25 % protein diet). In addition, in order to test whether these responses could involve a direct action of AA on the gene expression and activity of these enzymes, Caco-2/TC7 cells were cultured for 3 d with increasing AA concentrations. In vivo, in the ST, both high- and low-protein diets increased arginase activity in the intestinal mucosa (ST25 %: 46 (sem 2) μmol/g per min and ST10 %: 46 (sem 2) μmol/g per min v. ST17 %: 36 (sem 3) μmol/g per min, P < 0·05). In the LT, OAT expression was increased in the LT10 % group (+277 %, P < 0·05) compared with the LT17 % group. Caco-2/TC7 cells showed inverse relationships between AA supply and arginase (P = 0·058) and OAT (P = 0·035) expressions. The present study demonstrates the regulation of intestinal arginase and OAT expressions in response to protein supply. Our in vitro experiments further indicate a direct AA-induced regulation of the mRNA abundance of these enzymes. In situations of limited protein supply, this regulation would increase intestinal arginine catabolism and, possibly via a decrease in arginine portal release, decrease hepatic AA oxidation, thus promoting N sparing.

Methionine transmethylation and transsulfuration in the piglet gastrointestinal tract

Methionine is an indispensable sulfur amino acid that functions as a key precursor for the synthesis of homocysteine and cysteine. Studies in adult humans suggest that splanchnic tissues convert dietary methionine to homocysteine and cysteine by means of transmethylation and transsulfuration, respectively. Studies in piglets show that significant metabolism of dietary indispensable amino acids occurs in the gastrointestinal tissues (GIT), yet the metabolic fate of methionine in GIT is unknown. We show here that 20% of the dietary methionine intake is metabolized by the GIT in piglets implanted with portal and arterial catheters and fed milk formula. Based on analyses from intraduodenal and intravenous infusions of [1-(13)C]methionine and [(2)H(3)]methionine, we found that the whole-body methionine transmethylation and remethylation rates were significantly higher during duodenal than intravenous tracer infusion. First-pass splanchnic metabolism accounted for 18% and 43% of the whole-body transmethylation and remethylation, respectively. Significant transmethylation and transsulfuration was demonstrated in the GIT, representing approximately 27% and approximately 23% of whole-body fluxes, respectively. The methionine used by the GIT was metabolized into homocysteine (31%), CO(2) (40%), or tissue protein (29%). Cystathionine beta-synthase mRNA and activity was present in multiple GITs, including intestinal epithelial cells, but was significantly lower than liver. We conclude that the GIT consumes 20% of the dietary methionine and is a significant site of net homocysteine production. Moreover, the GITs represent a significant site of whole-body transmethylation and transsulfuration, and these two pathways account for a majority of methionine used by the GITs.