Leucine supplementation of a low-protein meal increases skeletal muscle and visceral tissue protein synthesis in neonatal pigs by stimulating mTOR-dependent translation initiation

Leucine Protects Against Skeletal Muscle Atrophy in Lipopolysaccharide-Challenged Rats

Skeletal muscle atrophy is a decrease in muscle mass that occurs when protein degradation exceeds protein synthesis. Leucine (Leu), an essential branched-chain amino acid in animal nutrition, regulates skeletal muscle protein metabolism. Two experiments were conducted to evaluate whether Leu could alleviate lipopolysaccharide (LPS)-induced skeletal muscle wasting by modulating skeletal muscle protein synthesis and degradation. A total of 24 rats were randomly allocated into three groups (n = 8): (1) non-challenged control; (2) LPS-challenged control; and (3) LPS +3.0% Leu. Rats were fed with control or Leu-supplemented (part of the casein was replaced with 3.0% Leu) diets throughout the trial and were injected intraperitoneally with sterile saline or LPS at days 6, 11, 16, and 21. On the morning of day 22, serum samples were collected and rats were then sacrificed for liver and muscle analysis. In vitro protein degradation, nuclear factor-κB (NF-κB) activity, and proteolytic enzyme activities of the muscles from immune-challenged rats were also measured. Our results showed that the LPS challenge resulted in not only enhanced serum interleukin-1 and liver C-reactive protein (CRP) concentrations but also decreased the average daily body weight gain and muscle fiber diameter. However, dietary Leu inclusion attenuated the increase in CRP level and the decrease in muscle fiber diameter. Importantly, the LPS challenge caused a significant elevation in the muscle proteolysis rate, but dietary Leu supplementation significantly blocked the muscle proteolysis. The mRNA expression of NF-κB, muscle atrophy F-box (MAFbx), and muscle ring finger 1 (MuRF1) was upregulated by the LPS challenge in gastrocnemius muscles, but was downregulated by Leu supplementation. Interestingly, when muscles from the LPS-challenged rats were incubated with Leu in vitro, proteasome-, calpain-, and cathepsin-L-dependent muscle proteolysis and NF-κB activity were decreased. Collectively, the data suggest that Leu supplementation could inhibit excessive skeletal muscle degradation, as well as enhance protein synthesis and, thus, attenuate the negative effects caused by the LPS-induced immune challenge.

Nontargeted LC-MS Metabolomics Approach for Metabolic Profiling of Plasma and Urine from Pigs Fed Branched Chain Amino Acids for Maximum Growth Performance

The metabolic response in plasma and urine of pigs when feeding an optimum level of branched chain amino acids (BCAAs) for best growth performance is unknown. The objective of the current study was to identify the metabolic phenotype associated with the BCAAs intake level that could be linked to the animal growth performance. Three dose-response studies were carried out to collect blood and urine samples from pigs fed increasing levels of Ile, Val, or Leu followed by a nontargeted LC-MS approach to characterize the metabolic profile of biofluids when dietary BCAAs are optimum for animal growth. Results showed that concentrations of plasma hypoxanthine and tyrosine (Tyr) were higher while concentrations of glycocholic acid, tauroursodeoxycholic acid, and taurocholic acid were lower when the dietary Ile was optimum. Plasma 3-methyl-2-oxovaleric acid and creatine were lower when dietary Leu was optimum. The optimum dietary Leu resulted in increased urinary excretion of ascorbic acid and choline and relatively decreased excretion of 2-aminoadipic acid, acetyl-dl-valine, Ile, 2-methylbutyrylglycine, and Tyr. In conclusion, plasma glycocholic acid and taurocholic acid were discriminating metabolites to the optimum dietary Ile. The optimum dietary Leu was associated with reduced plasma creatine and urinary 2-aminoadipic acid and elevated urinary excretion of ascorbic acid and choline. The optimum dietary Val had a less pronounced metabolic response reflected in plasma or urine than other BCAA.

Enteral β-hydroxy-β-methylbutyrate supplementation increases protein synthesis in skeletal muscle of neonatal pigs

Many low-birth weight infants are at risk for poor growth due to an inability to achieve adequate protein intake. Administration of the amino acid leucine stimulates protein synthesis in skeletal muscle of neonates. To determine the effects of enteral supplementation of the leucine metabolite β-hydroxy-β-methylbutyrate (HMB) on protein synthesis and the regulation of translation initiation and degradation pathways, overnight-fasted neonatal pigs were studied immediately (F) or fed one of five diets for 24 h: low-protein (LP), high-protein (HP), or LP diet supplemented with 4 (HMB4), 40 (HMB40), or 80 (HMB80) μmol HMB·kg body wt(-1)·day(-1) Cell replication was assessed from nuclear incorporation of BrdU in the longissimus dorsi (LD) muscle and jejunum crypt cells. Protein synthesis rates in LD, gastrocnemius, rhomboideus, and diaphragm muscles, lung, and brain were greater in HMB80 and HP and in brain were greater in HMB40 compared with LP and F groups. Formation of the eIF4E·eIF4G complex and S6K1 and 4E-BP1 phosphorylation in LD, gastrocnemius, and rhomboideus muscles were greater in HMB80 and HP than in LP and F groups. Phosphorylation of eIF2α and eEF2 and expression of SNAT2, LAT1, MuRF1, atrogin-1, and LC3-II were unchanged. Numbers of BrdU-positive myonuclei in the LD were greater in HMB80 and HP than in the LP and F groups; there were no differences in jejunum. The results suggest that enteral supplementation with HMB increases skeletal muscle protein anabolism in neonates by stimulation of protein synthesis and satellite cell proliferation.

Supplementation of branched-chain amino acids to a reduced-protein diet improves growth performance in piglets: involvement of increased feed intake and direct muscle growth-promoting effect

The aim of this study was to investigate whether supplementing branched-chain amino acids (AA) (BCAA) along with a reduced-protein diet increases piglet growth, and whether elevated feed intake and muscle growth-promoting effect contribute to this improvement. In Expt 1, twenty-eight weanling piglets were randomly fed one of the following four diets: a positive control (PC) diet, a reduced-protein negative control (NC) diet, an NC diet supplemented with BCAA to the same levels as in the PC diet (test 1 (T1)) and an NC diet supplemented with a 2-fold dose of BCAA in T1 diet (test 2 (T2)) for 28 d. In Expt 2, twenty-one weanling piglets were randomly assigned to NC, T1 and pair-fed T1 (P) groups. NC and T1 diets were the same as in Expt 1, whereas piglets in the P group were individually pair-fed with the NC group. In Expt 1, the NC group had reduced piglet growth and feed intake compared with the PC group, which were restored in T1 and T2 groups, but no differences were detected between T1 and T2 groups. In Expt 2, T1 and P groups showed increases in growth and mass of some muscles compared with the NC group. Increased feed intake after BCAA supplementation was associated with increased mRNA expressions of agouti-related peptide and co-express neuropeptide Y (NPY) and phosphorylation of mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase 1 (S6K1), as well as decreased mRNA expressions of melanocortin-4 receptor and cocaine- and amphetamine-regulated transcript and phosphorylation of eukaryotic initiation factor 2α in the hypothalamus. No differences were observed among PC, T1 and T2 groups except for higher NPY mRNA expression in the T2 group than in the PC group (Expt 1). Phosphorylation of mTOR and S6K1 in muscle was enhanced after BCAA supplementation, which was independent of change in feed intake (Expt 2). In conclusion, supplementing BCAA to reduced-protein diets increases feed intake and muscle mass, and contributes to better growth performance in piglets.

Pulsatile delivery of a leucine supplement during long-term continuous enteral feeding enhances lean growth in term neonatal pigs

Neonatal pigs are used as a model to study and optimize the clinical treatment of infants who are unable to maintain oral feeding. Using this model, we have shown previously that pulsatile administration of leucine during continuous feeding over 24 h via orogastric tube enhanced protein synthesis in skeletal muscle compared with continuous feeding alone. To determine the long-term effects of leucine pulses, neonatal piglets (n = 11-12/group) were continuously fed formula via orogastric tube for 21 days, with an additional parenteral infusion of either leucine (CON + LEU; 800 μmol·kg^-1·h^-1) or alanine (CON + ALA) for 1 h every 4 h. The results show that body and muscle weights and lean gain were ∼25% greater, and fat gain was 48% lower in CON + LEU than CON + ALA; weights of other tissues were unaffected by treatment. Fractional protein synthesis rates in longissimus dorsi, gastrocnemius, and soleus muscles were ∼30% higher in CON + LEU compared with CON + ALA and were associated with decreased Deptor abundance and increased mTORC1, mTORC2, 4E-BP1, and S6K1 phosphorylation, SNAT2 abundance, and association of eIF4E with eIF4G and RagC with mTOR. There were no treatment effects on PKB, eIF2α, eEF2, or PRAS40 phosphorylation, Rheb, SLC38A9, v-ATPase, LAMTOR1, LAMTOR2, RagA, RagC, and LAT1 abundance, the proportion of polysomes to nonpolysomes, or the proportion of mRNAs encoding rpS4 or rpS8 associated with polysomes. Our results demonstrate that pulsatile delivery of a leucine supplement during 21 days of continuous enteral feeding enhances lean growth by stimulating the mTORC1-dependent translation initiation pathway, leading to protein synthesis in skeletal muscle of neonates.

Leucine supplementation of a chronically restricted protein and energy diet enhances mTOR pathway activation but not muscle protein synthesis in neonatal pigs

Suboptimal nutrient intake represents a limiting factor for growth and long-term survival of low-birth weight infants. The objective of this study was to determine if in neonates who can consume only 70 % of their protein and energy requirements for 8 days, enteral leucine supplementation will upregulate the mammalian target of rapamycin (mTOR) pathway in skeletal muscle, leading to an increase in protein synthesis and muscle anabolism. Nineteen 4-day-old piglets were fed by gastric tube 1 of 3 diets, containing (kg body weight(-1) · day(-1)) 16 g protein and 190 kcal (CON), 10.9 g protein and 132 kcal (R), or 10.8 g protein + 0.2 % leucine and 136 kcal (RL) at 4-h intervals for 8 days. On day 8, plasma AA and insulin levels were measured during 6 post-feeding intervals, and muscle protein synthesis rate and mTOR signaling proteins were determined at 120 min post-feeding. At 120 min, leucine was highest in RL (P < 0.001), whereas insulin, isoleucine and valine were lower in RL and R compared to CON (P < 0.001). Compared to RL and R, the CON diet increased (P < 0.01) body weight, protein synthesis, phosphorylation of S6 kinase (p-S6K1) and 4E-binding protein (p-4EBP1), and activation of eukaryotic initiation factor 4 complex (eIF4E · eIF4G). RL increased (P ≤ 0.01) p-S6K1, p-4EBP1 and eIF4E · eIF4G compared to R. In conclusion, when protein and energy intakes are restricted for 8 days, leucine supplementation increases muscle mTOR activation, but does not improve body weight gain or enhance skeletal muscle protein synthesis in neonatal pigs.

Effects of dietary leucine supplementation in low crude protein diets on performance, nitrogen balance, whole-body protein turnover, carcass characteristics and meat quality of finishing pigs

Eighteen Duroc × Landrace × Yorkshire barrows, with an average initial body weight (BW) of 75.4 ± 2.0 kg, were randomly allotted to one of three diets with six replicates per treatment for 25 days. The diets comprised a normal protein diet (NP, 14.5% crude protein), a low crude protein diet supplemented with 0.27% alanine (LP + Ala, 10.0% crude protein), or a low crude protein diet supplemented with 0.40% leucine (LP + Leu, 10.0% crude protein). The whole-body protein synthesis rate, whole-body protein breakdown rate and protein deposition rate in pigs fed the LP + Leu diet were similar to the NP diet (P > 0.05), and both were significantly higher than pigs fed the LP + Ala diet (P < 0.05). The Longissimus muscle area (LMA) of pigs fed the LP + Leu diet was larger than those fed the LP + Ala diet (P = 0.05). In addition, drip loss and intramuscular fat of pigs fed the LP + Ala diet were higher than that of the others (P < 0.05). In conclusion, supplementation of leucine in low protein diet could stimulate protein deposition and improve the meat quality of finishing pigs more than an alanine-supplemented one.

Effects of dietary leucine supplementation on the gene expression of mammalian target of rapamycin signaling pathway and intestinal development of broilers

This experiment was to investigate the effects of dietary leucine supplementation on the gene expression of mammalian target of rapamycin (mTOR) signaling pathway and intestinal development of broilers. A total of 384 one-day-old broilers were randomly assigned into 4 treatments with 6 replicates (16 broilers per replicate). Broilers in these treatment groups were offered the following diets with 1.37, 1.77, 2.17 and 2.57% of leucine. These diet treatments were named 1.37TM, 1.77TM, 2.17TM, and 2.57TM. The experiment lasted 21 days and all birds had free access to feed and water. Results indicated that there was no significant difference in body weight, average daily gain and average feed intake among all treatments (P > 0.05). The broiler duodenal villus height in 2.57TM was the lowest, but the highest occurred in 1.37TM on d 7 and 14 (P < 0.05). The villus height in the jejunum and ileum increased along with leucine level from 1.37 to 2.17%. The villus height of jejunum was significantly higher in 2.17TM than in 1.37TM on d 7 and 14, and the ratio of villus height to crypt depth (V:C) in the duodenum, jejunum and ileum increased significantly (P < 0.05) on d 21. The gene expression level of mTOR in the duodenum decreased with increasing leucine level and was higher in 1.37TM than in 2.57TM on d 7 and 14 (P < 0.05). On d 14 and 21 of the trial, the expression of S6K1 in the duodenum was higher in 1.37TM than in 2.57TM (P < 0.05), and the expression of mTOR, S6K1 in the jejunum and ileum increased with increasing leucine level form 1.37 to 2.17%, whereas a significant difference occurred between 1.37TM and 2.17TM (P < 0.05). In conclusion, the addition of leucine fails to enhance the growth performance of broilers. However, leucine can improve intestinal development by enhancing villus height and V:C ratio in the jejunum and ileum. Moreover, the expression of mTOR, S6K1 increased as the level of dietary leucine was elevated from 1.37 to 2.17%.

Impact of prolonged leucine supplementation on protein synthesis and lean growth in neonatal pigs

Most low-birth weight infants experience extrauterine growth failure due to reduced nutrient intake as a result of feeding intolerance. The objective of this study was to determine whether prolonged enteral leucine supplementation improves lean growth in neonatal pigs fed a restricted protein diet. Neonatal pigs (n = 14-16/diet, 5 days old, 1.8 ± 0.3 kg) were fed by gastric catheter a whey-based milk replacement diet with either a high protein (HP) or restricted protein (RP) content or RP supplemented with leucine to the same level as in the HP diet (RPL). Pigs were fed 40 ml·kg body wt(-1)·meal(-1) every 4 h for 21 days. Feeding the HP diet resulted in greater total body weight and lean body mass compared with RP-fed pigs (P < 0.05). Masses of the longissimus dorsi muscle, heart, and kidneys were greater in the HP- than RP-fed pigs (P < 0.05). Body weight, lean body mass, and masses of the longissimus dorsi, heart, and kidneys in pigs fed the RPL diet were intermediate to RP- and HP-fed pigs. Protein synthesis and mTOR signaling were increased in all muscles with feeding (P < 0.05); leucine supplementation increased mTOR signaling and protein synthesis rate in the longissimus dorsi (P < 0.05). There was no effect of diet on indices of protein degradation signaling in any tissue (P > 0.05). Thus, when protein intake is chronically restricted, the capacity for leucine supplementation to enhance muscle protein accretion in neonatal pigs that are meal-fed milk protein-based diets is limited.

Dietary Leucine Supplementation Improves the Mucin Production in the Jejunal Mucosa of the Weaned Pigs Challenged by Porcine Rotavirus

The present study was mainly conducted to determine whether dietary leucine supplementation could attenuate the decrease of the mucin production in the jejunal mucosa of weaned pigs infected by porcine rotavirus (PRV). A total of 24 crossbred barrows weaned at 21 d of age were assigned randomly to 1 of 2 diets supplemented with 1.00% L-leucine or 0.68% L-alanine (isonitrogenous control) for 17 d. On day 11, all pigs were orally infused PRV or the sterile essential medium. During the first 10 d of trial, dietary leucine supplementation could improve the feed efficiency (P = 0.09). The ADG and feed efficiency were impaired by PRV infusion (P<0.05). PRV infusion also increased mean cumulative score of diarrhea, serum rotavirus antibody concentration and crypt depth of the jejunal mucosa (P<0.05), and decreased villus height: crypt depth (P = 0.07), goblet cell numbers (P<0.05), mucin 1 and 2 concentrations (P<0.05) and phosphorylated mTOR level (P<0.05) of the jejunal mucosa in weaned pigs. Dietary leucine supplementation could attenuate the effects of PRV infusion on feed efficiency (P = 0.09) and mean cumulative score of diarrhea (P = 0.09), and improve the effects of PRV infusion on villus height: crypt depth (P = 0.06), goblet cell numbers (P<0.05), mucin 1 (P = 0.08) and 2 (P = 0.07) concentrations and phosphorylated mTOR level (P = 0.08) of the jejunal mucosa in weaned pigs. These results suggest that dietary 1% leucine supplementation alleviated the decrease of mucin production and goblet cell numbers in the jejunal mucosa of weaned pigs challenged by PRV possibly via activation of the mTOR signaling.

Enteral delivery of proteins enhances the expression of proteins involved in the cytoskeleton and protein biosynthesis in human duodenal mucosa

BACKGROUND

Amino acids are well known to be key effectors of gut protein turnover. We recently reported that enteral delivery of proteins markedly stimulated global duodenal protein synthesis in carbohydrate-fed healthy humans, but specifically affected proteins remain unknown.

OBJECTIVE

We aimed to assess the influence of an enteral protein supply on the duodenal mucosal proteome in carbohydrate-fed humans.

DESIGN

Six healthy volunteers received for 5 h, on 2 occasions and in random order, either an enteral infusion of maltodextrins alone (0.25 g · kg⁻¹ · h⁻¹) mimicking the fed state or maltodextrins with a protein powder (0.14 g proteins · kg⁻¹ · h⁻¹). Endoscopic duodenal biopsy specimens were then collected and frozen until analysis. A 2-dimensional polyacrylamide gel electrophoresis-based comparative proteomics analysis was then performed, and differentially expressed proteins (at least ±1.5-fold change; Student's t test, P < 0.05) were identified by mass spectrometry. Protein expression changes were confirmed by Western blot analysis.

RESULTS

Thirty-two protein spots were differentially expressed after protein delivery compared with maltodextrins alone: 28 and 4 spots were up- or downregulated, respectively. Among the 22 identified proteins, 11 upregulated proteins were involved either in the cytoskeleton (ezrin, moesin, plastin 1, lamin B1, vimentin, and β-actin) or in protein biosynthesis (glutamyl-prolyl-transfer RNA synthetase, glutaminyl-transfer RNA synthetase, elongation factor 2, elongation factor 1δ, and eukaryotic translation and initiation factor 3 subunit f).

CONCLUSIONS

Enteral delivery of proteins altered the duodenal mucosal proteome and mainly stimulated the expression of proteins involved in cytoskeleton and protein biosynthesis. These results suggest that protein supply may affect intestinal morphology by stimulating actin cytoskeleton remodeling.

Enzymatically Modified Starch Ameliorates Postprandial Serum Triglycerides and Lipid Metabolome in Growing Pigs

Developing host digestion-resistant starches to promote human health is of great research interest. Chemically modified starches (CMS) are widely used in processed foods and although the modification of the starch molecule allows specific reduction in digestibility, the metabolic effects of CMS have been less well described. This short-term study evaluated the impact of enzymatically modified starch (EMS) on fasting and postprandial profiles of blood glucose, insulin and lipids, and serum metabolome in growing pigs. Eight jugular-vein catheterized pigs (initial body weight, 37.4 kg; 4 months of age) were fed 2 diets containing 72% purified starch (EMS or waxy corn starch (control)) in a cross-over design for 7 days. On day 8, an 8-hour meal tolerance test (MTT) was performed with serial blood samplings. Besides biochemical analysis, serum was analysed for 201 metabolites through targeted mass spectrometry-based metabolomic approaches. Pigs fed the EMS diet showed increased (P<0.05) immediate serum insulin and plasma glucose response compared to pigs fed the control diet; however, area-under-the-curves for insulin and glucose were not different among diets. Results from MTT indicated reduced postprandial serum triglycerides with EMS versus control diet (P<0.05). Likewise, serum metabolome profiling identified characteristic changes in glycerophospholipid, lysophospholipids, sphingomyelins and amino acid metabolome profiles with EMS diet compared to control diet. Results showed rapid adaptations of blood metabolites to dietary starch shifts within 7 days. In conclusion, EMS ingestion showed potential to attenuate postprandial raise in serum lipids and suggested constant alteration in the synthesis or breakdown of sphingolipids and phospholipids which might be a health benefit of EMS consumption. Because serum insulin was not lowered, more research is warranted to reveal possible underlying mechanisms behind the observed changes in the profile of serum lipid metabolome in response to EMS consumption.

Maternal Diabetes Leads to Adaptation in Embryonic Amino Acid Metabolism during Early Pregnancy

During pregnancy an adequate amino acid supply is essential for embryo development and fetal growth. We have studied amino acid composition and branched chain amino acid (BCAA) metabolism at day 6 p.c. in diabetic rabbits and blastocysts. In the plasma of diabetic rabbits the concentrations of 12 amino acids were altered in comparison to the controls. Notably, the concentrations of the BCAA leucine, isoleucine and valine were approximately three-fold higher in diabetic rabbits than in the control. In the cavity fluid of blastocysts from diabetic rabbits BCAA concentrations were twice as high as those from controls, indicating a close link between maternal diabetes and embryonic BCAA metabolism. The expression of BCAA oxidizing enzymes and BCAA transporter was analysed in maternal tissues and in blastocysts. The RNA amounts of three oxidizing enzymes, i.e. branched chain aminotransferase 2 (Bcat2), branched chain ketoacid dehydrogenase (Bckdha) and dehydrolipoyl dehydrogenase (Dld), were markedly increased in maternal adipose tissue and decreased in liver and skeletal muscle of diabetic rabbits than in those of controls. Blastocysts of diabetic rabbits revealed a higher Bcat2 mRNA and protein abundance in comparison to control blastocysts. The expression of BCAA transporter LAT1 and LAT2 were unaltered in endometrium of diabetic and healthy rabbits, whereas LAT2 transcripts were increased in blastocysts of diabetic rabbits. In correlation to high embryonic BCAA levels the phosphorylation amount of the nutrient sensor mammalian target of rapamycin (mTOR) was enhanced in blastocysts caused by maternal diabetes. These results demonstrate a direct impact of maternal diabetes on BCAA concentrations and degradation in mammalian blastocysts with influence on embryonic mTOR signalling.

Leucine is a major regulator of muscle protein synthesis in neonates

Approximately 10% of infants born in the United States are of low birth weight. Growth failure during the neonatal period is a common occurrence in low birth weight infants due to their inability to tolerate full feeds, concerns about advancing protein supply, and high nutrient requirements for growth. An improved understanding of the nutritional regulation of growth during this critical period of postnatal growth is vital for the development of strategies to improve lean gain. Past studies with animal models have demonstrated that muscle protein synthesis is increased substantially following a meal and that this increase is due to the postprandial rise in amino acids as well as insulin. Both amino acids and insulin act independently to stimulate protein synthesis in a mammalian target of rapamycin-dependent manner. Further studies have elucidated that leucine, in particular, and its metabolites, α-ketoisocaproic acid and β-hydroxy-β-methylbutyrate, have unique anabolic properties. Supplementation with leucine, provided either parenterally or enterally, has been shown to enhance muscle protein synthesis in neonatal pigs, making it an ideal candidate for stimulating growth of low birth weight infants.

Bolus vs. continuous feeding to optimize anabolism in neonates

PURPOSE OF REVIEW

Neonates with feeding difficulties can be fed by orogastric tube, using either continuous or bolus delivery. This review reports on recent findings that bolus is advantageous compared to continuous feeding in supporting optimal protein anabolism.

RECENT FINDINGS

Whether bolus or continuous feeding is more beneficial has been controversial, largely due to limitations inherent in clinical studies, such as the presence of confounding variables and the inability to use invasive approaches. Recent studies using the piglet as a model of the human neonate showed that, compared to continuous feeding, bolus feeding enhances protein synthesis and promotes greater protein deposition. The increase in protein synthesis occurs in muscles of varying fiber type and in visceral tissues whereas muscle protein degradation is largely insensitive to feeding pattern. This higher protein synthesis rate is enabled by the rapid and profound increases in circulating amino acids and insulin that occur following a bolus feed, which activate the intracellular signaling pathways leading to mRNA translation.

SUMMARY

Recent findings indicate that bolus feeding enhances protein synthesis more than continuous feeding and promotes greater protein anabolism. The difference in response is attributable to the pulsatile pattern of amino acid-induced and insulin-induced translation initiation induced only by bolus feeding.

Maternal low-protein diet affects myostatin signaling and protein synthesis in skeletal muscle of offspring piglets at weaning stage

PURPOSE

We tested the hypothesis that maternal low-protein (LP) diet during gestation and lactation can program myostatin (MSTN) signaling and protein synthesis in skeletal muscle of offspring at weaning stage (35 days).

METHODS

Fourteen Meishan sows were fed either LP or standard-protein diets throughout gestation and lactation, male offspring piglets were killed at weaning stage and longissimus dorsi (LD) muscles were taken. The cross-sectional areas (CSA) of LD muscles were measured by hematoxylin and eosin staining. The levels of free amino acids in plasma were measured by amino acid auto-analyzer. Proteins and mRNA were determined by Western blot and RT-qPCR, respectively.

RESULTS

Body weight, LD muscle weight and the myofiber CSA were significantly decreased (P < 0.05) in LP piglets; meanwhile, the concentration of branched-chain amino acids was also significantly decreased (P < 0.001). MSTN protein content tended to be higher (P = 0.098) in LP piglets, while the expression of MSTN receptors, activin type II receptor-beta and transforming growth factor type-beta type I receptor kinase, was significantly up-regulated (P < 0.05). Furthermore, p38 mitogen-activated protein kinase, the downstream signaling factor of MSTN, was also enhanced significantly (P < 0.05). In addition, key factors of translation initiation, phosphorylated eukaryotic initiation factor 4E and the 70 kDa ribosomal protein S6 kinase, were significantly decreased (P < 0.05) in LP piglets.

CONCLUSIONS

Our results suggest that maternal LP diet during gestation and lactation affects MSTN signaling and protein synthesis in skeletal muscle of offspring at weaning stage.

Leucine stimulates ASCT2 amino acid transporter expression in porcine jejunal epithelial cell line (IPEC-J2) through PI3K/Akt/mTOR and ERK signaling pathways

Leucine has been shown to influence intestinal protein metabolism, cell proliferation and migration. Furthermore, our previous study demonstrated that branched-chain amino acids could modulate the intestinal amino acid and peptide transporters in vivo. As the possible mechanisms are still largely unknown, in the present work, we studied the transcriptional and translational regulation of leucine on amino acid transporter production in IPEC-J2 cells and the signaling pathways involved. Treatment of IPEC-J2 cells with 7.5 mM leucine enhanced the mRNA expression of the Na(+)-neutral AA exchanger 2 (ASCT2) and 4F2 heavy chain (4F2hc) and caused an increase in ASCT2 protein expression. Leucine also activated phosphorylation of 4E-BP1 and eIF4E through the phosphorylation of mTOR, Akt and ERK signaling pathways in IPEC-J2 cells. Pre-treatment of IPEC-J2 cells with inhibitors of mTOR and Akt (rapamycin and wortmannin) or an inhibitor of ERK (PD098059) for 30 min before leucine treatment attenuated the positive effect of leucine in enhancing the protein abundance of ASCT2. These results demonstrate that leucine could up-regulate the expression of the amino acid transporters (ASCT2) through transcriptional and translational regulation by ERK and PI3K/Akt/mTOR activation.

Beyond the role of dietary protein and amino acids in the prevention of diet-induced obesity

High-protein diets have been shown to prevent the development of diet-induced obesity and can improve associated metabolic disorders in mice. Dietary leucine supplementation can partially mimic this effect. However, the molecular mechanisms triggering these preventive effects remain to be satisfactorily explained. Here we review studies showing a connection between high protein or total amino nitrogen intake and obligatory water intake. High amino nitrogen intake may possibly lower lipid storage, and prevent insulin resistance. Suggestions are made for further systematical studies to explore the relationship between water consumption, satiety, and energy expenditure. Moreover, these examinations should better distinguish between leucine-specific and unspecific effects. Research in this field can provide important information to justify dietary recommendations and strategies in promoting long-term weight loss and may help to reduce health problems associated with the comorbidities of obesity.

Leucine supplementation improves skeletal muscle regeneration after cryolesion in rats

This study was undertaken in order to provide further insight into the role of leucine supplementation in the skeletal muscle regeneration process, focusing on myofiber size and strength recovery. Young (2-month-old) rats were subjected or not to leucine supplementation (1.35 g/kg per day) started 3 days prior to cryolesion. Then, soleus muscles were cryolesioned and continued receiving leucine supplementation until 1, 3 and 10 days later. Soleus muscles from leucine-supplemented animals displayed an increase in myofiber size and a reduction in collagen type III expression on post-cryolesion day 10. Leucine was also effective in reducing FOXO3a activation and ubiquitinated protein accumulation in muscles at post-cryolesion days 3 and 10. In addition, leucine supplementation minimized the cryolesion-induced decrease in tetanic strength and increase in fatigue in regenerating muscles at post-cryolesion day 10. These beneficial effects of leucine were not accompanied by activation of any elements of the phosphoinositide 3-kinase/Akt/mechanistic target of rapamycin signalling pathway in the regenerating muscles. Our results show that leucine improves myofiber size gain and strength recovery in regenerating soleus muscles through attenuation of protein ubiquitination. In addition, leucine might have therapeutic effects for muscle recovery following injury and in some muscle diseases.

Protein synthesis in skeletal muscle of neonatal pigs is enhanced by administration of β-hydroxy-β-methylbutyrate

Many low-birth-weight infants experience failure to thrive. The amino acid leucine stimulates protein synthesis in skeletal muscle of the neonate, but less is known about the effects of the leucine metabolite β-hydroxy-β-methylbutyrate (HMB). To determine the effects of HMB on protein synthesis and the regulation of translation initiation and degradation pathways, overnight-fasted neonatal pigs were infused with HMB at 0, 20, 100, or 400 μmol·kg body wt(-1)·h(-1) for 1 h (HMB 0, HMB 20, HMB 100, or HMB 400). Plasma HMB concentrations increased with infusion and were 10, 98, 316, and 1,400 nmol/ml in the HMB 0, HMB 20, HMB 100, and HMB 400 pigs. Protein synthesis rates in the longissimus dorsi (LD), gastrocnemius, soleus, and diaphragm muscles, lung, and spleen were greater in HMB 20 than in HMB 0, and in the LD were greater in HMB 100 than in HMB 0. HMB 400 had no effect on protein synthesis. Eukaryotic initiation factor (eIF)4E·eIF4G complex formation and ribosomal protein S6 kinase-1 and 4E-binding protein-1 phosphorylation increased in LD, gastrocnemius, and soleus muscles with HMB 20 and HMB 100 and in diaphragm with HMB 20. Phosphorylation of eIF2α and elongation factor 2 and expression of system A transporter (SNAT2), system L transporter (LAT1), muscle RING finger 1 protein (MuRF1), muscle atrophy F-box (atrogin-1), and microtubule-associated protein light chain 3 (LC3-II) were unchanged. Results suggest that supplemental HMB enhances protein synthesis in skeletal muscle of neonates by stimulating translation initiation.

Isoleucine, leucine, methionine, and threonine effects on mammalian target of rapamycin signaling in mammary tissue

Improved representation of postabsorptive N metabolism in lactating dairy cows requires a better understanding of protein synthesis regulation in the mammary glands. This study aimed to determine the quantitative effects of Ile, Leu, Met, and Thr on the phosphorylation state of signaling proteins that regulate protein synthesis. The experiment used a composite design with a central point, 2 axial points per AA, and a complete 2(4) factorial. All of the other AA were provided at the concentrations in Dulbecco's modified Eagle's medium. The experiment was replicated with tissues from 5 lactating cows. Mammary tissue slices (0.12 ± 0.02 g) were incubated for 4h. Total and site-specific phosphorylated mammalian target of rapamycin (mTOR; Ser2448), eukaryotic elongation factor (eEF) 2 (Thr56), ribosomal protein S6 (Ser235/236), and eukaryotic initiation factor 2α (Ser51) were determined by western immunoblotting. Tissue concentrations of the 4 AA studied responded linearly to media supply. Addition of Ile, Leu, Met, or Thr had no effect on eukaryotic initiation factor 2α phosphorylation. Isoleucine and Thr positively affected mTOR phosphorylation. However, the 2 AA had an antagonistic relationship. Similarly, Ile linearly increased ribosomal protein S6 phosphorylation, and Thr inhibited the Ile effect. In addition, eEF2 phosphorylation was linearly decreased by Ile and Leu. Threonine curvilinearly decreased eEF2 phosphorylation, Ile and Leu negatively interacted on eEF2, and Thr tended to inhibit Leu effects on eEF2. This work demonstrated saturable responses and interactions between AA on activation of the mTOR pathway. Incorporation of these concepts into milk protein response models will help to improve milk and milk protein yield predictions and increase postabsorptive N efficiency and reduce N excretion by dairy cows.

Leucine pulses enhance skeletal muscle protein synthesis during continuous feeding in neonatal pigs

Infants unable to maintain oral feeding can be nourished by orogastric tube. We have shown that orogastric continuous feeding restricts muscle protein synthesis compared with intermittent bolus feeding in neonatal pigs. To determine whether leucine infusion can be used to enhance protein synthesis during continuous feeding, neonatal piglets received the same amount of formula enterally by orogastric tube for 25.25 h continuously (CON) with or without LEU or intermittently by bolus every 4 h (BOL). For the CON+LEU group, leucine pulses were administered parenterally (800 μmol·kg(-1)·h(-1)) every 4 h. Insulin and glucose concentrations increased after the BOL meal and were unchanged in groups fed continuously. LEU infusion during CON feeding increased plasma leucine after the leucine pulse and decreased essential amino acids compared with CON feeding. Protein synthesis in longissimus dorsi (LD), gastrocnemius, and soleus muscles, but not liver or heart, were greater in CON+LEU and BOL than in the CON group. BOL feeding increased protein synthesis in the small intestine. Muscle S6K1 and 4E-BP1 phosphorylation and active eIF4E·eIF4G complex formation were higher in CON+LEU and BOL than in CON but AMPKα, eIF2α, and eEF2 phosphorylation were unchanged. LC3-II-to-total LC3 ratio was lower in CON+LEU and BOL than in CON, but there were no differences in atrogin-1 and MuRF-1 abundance and FoxO3 phosphorylation. In conclusion, administration of leucine pulses during continuous orogastric feeding in neonates increases muscle protein synthesis by stimulating translation initiation and may reduce protein degradation via the autophagy-lysosome, but not the ubiquitin-proteasome pathway.

Enteral delivery of proteins stimulates protein synthesis in human duodenal mucosa in the fed state through a mammalian target of rapamycin-independent pathway

BACKGROUND

Glutamine modulates duodenal protein metabolism in fasted healthy humans, but its effects in a fed state remain unknown.

OBJECTIVE

We aimed to assess the effects of either glutamine or an isonitrogenous protein mixture on duodenal protein metabolism in humans in the fed state.

DESIGN

Twenty-four healthy volunteers were randomly included in 2 groups. Each volunteer was studied on 2 occasions in a random order and received, during 5 h, either an enteral infusion of maltodextrins alone (0.25 g · kg⁻¹ · h⁻¹; both groups) that mimicked a carbohydrate fed state or maltodextrins with glutamine (group 1) or an isonitrogenous (22.4 mg N · kg⁻¹ · h⁻¹) protein powder (group 2). Simultaneously, a continuous intravenous infusion of ¹³C-leucine and ²H₅-phenylalanine (both 9 μmol · kg⁻¹ · h⁻¹) was performed. Endoscopic duodenal biopsies were taken. Leucine and phenylalanine enrichments were assessed by using gas chromatography-mass spectrometry in duodenal proteins and the intracellular free amino acids pool to calculate the mucosal fractional synthesis rate (FSR). Proteasome proteolytic activities and phosphokinase expression were assessed by using specific fluorogenic substrates and macroarrays, respectively.

RESULTS

The FSR and proteasome activity were not different after the glutamine supply compared with after maltodextrins alone. In contrast, the FSR increased (1.7-fold increase; P < 0.05) after protein-powder delivery without modification of total proteasome activity. The protein powder increased insulinemia, PI3 kinase, and erk phosphorylation but did not affect the mammalian target of rapamycin (mTOR) pathway and mitogen-activated protein kinase signal-integrating kinase 1 phosphorylation. A trend for an increase of eukaryotic translation initiation factor 4E phosphorylation was observed (P = 0.07).

CONCLUSION

In the carbohydrate fed state, enteral proteins but not glutamine increased duodenal protein synthesis through an mTOR independent pathway in humans.

An enteral leucine supply modulates human duodenal mucosal proteome and decreases the expression of enzymes involved in fatty acid beta-oxidation

Leucine is well known to regulate protein metabolism in muscle. We recently reported that enteral leucine infusion decreased proteasome activity in human duodenal mucosa and enhanced intestinal cell proliferation, but its effects on gut proteome remain unknown. Therefore, we aimed to assess the effects of an enteral leucine infusion on the whole proteome of duodenal mucosa. In this work, 5 healthy volunteers received for 5h, on 2 occasions and in random order, an enteral supply of maltodextrins (0.25 g kg(-1) h(-1)) or maltodextrins supplemented with leucine (0.035 g kg(-1) h(-1)). At the end of infusion, endoscopic duodenal biopsy samples were collected and analyzed by 2D-PAGE. Eleven protein spots were differentially and significantly (P<0.05) expressed in response to the leucine-supplemented maltodextrins compared with maltodextrins alone. Forty percent of identified proteins by mass spectrometry were located in mitochondria. Four proteins were involved in lipid metabolism: HADHA, ACADVL and CPT2 expressions were reduced, whereas FABP1 expression was increased. In addition, the expression of DHA kinase involved in glycerol metabolism was also downregulated. Finally, leucine supplementation altered the duodenal mucosal proteome by regulating the expression of several enzymes mainly involved in lipid metabolism. These results suggest that leucine supplementation may slowdown fatty acid beta-oxidation in human duodenal mucosa.

New perspectives in the control of body protein metabolism

Recent advances in elucidating the mechanisms that control body protein synthesis and degradation both expand and complicate our understanding of how these processes are regulated. This review presents an introduction to the multiple regulatory systems involved, emphasizing the number of potential controls. These include gene transcription, gene activation or suppression, activation or suppression of mRNA translation and activation or suppression of signaling pathways. The complexity of these interacting controls presents a challenge to our understanding of the overall coordinated regulation of protein synthesis and degradation and its response to any particular stimulus. Specific examples are used to illustrate regulatory mechanisms, including the ways in which protein metabolism is regulated by the amino acid leucine. In addition to regulation associated with gene expression and post-translational control, the expanding field of epigenetics adds another layer of complexity, including trans-generational responses to nutrient intake, highlighting the potential for long-term impact of nutritional experience on the metabolism of subsequent generations.

Inhibition of mammalian target of rapamycin signaling by CCI-779 (temsirolimus) induces growth inhibition and cell cycle arrest in Cashmere goat fetal fibroblasts (Capra hircus)

The mammalian target of rapamycin (mTOR) is a Ser/Thr kinase. It plays an evolutionarily conserved role in regulating cell growth, proliferation, survival, and metabolism via different cellular processes. The purpose of this study was to explore the inhibitory effects of CCI-779 (temsirolimus), a specific mTOR inhibitor, on mTOR signaling, and examine the mechanism of cell growth suppression by CCI-779 in Cashmere goat fetal fibroblasts (GFb cells). GFb cells were sensitive to CCI-779 and the survival rate of cells treated with >3.0 μM of CCI-779 was significantly reduced compared with the control (p<0.01). CCI-779 inhibited the phosphorylation of mTOR (at Ser2448) and S6 (at Ser240/244), and the expression of mTOR, p70S6K, and S6. Thus, CCI-779 was toxic to GFb cells, and it induced a dose-dependent decrease in cell proliferation and caused G1/S cell cycle arrest. Taken together, these data show that CCI-779 can inhibit mTOR signaling and proliferation in GFb cells in vitro. Therefore, mTOR is an important regulator for GFb cell growth and proliferation.

Towards amino acid recommendations for specific physiological and patho-physiological states in pigs

The objective of this review is to provide an overview of the implication of amino acids (AA) in important physiological functions. This is done in the context of pig production where the competition for AA utilisation is exacerbated by constraints to maximise productive responses and the necessity to reduce dietary protein input for environmental, economic and sanitary issues. Therefore, there is an opportunity to refine the nutritional recommendations by exploring the physiological roles of AA. For example, methionine and cysteine, either in selenised or sulfur forms, are directly involved in the regulation of the glutathione antioxidative system. In sows, glutathione antioxidative system may contribute to improving ovulation conditions through control of oxidative pressure. Supplementation of sow diets withl-arginine, a precursor of NO and polyamines, may stimulate placental growth, promoting conceptus survival, growth and tissue development. The beneficial effect of arginine supplementation has been also suggested to improve lactation performance. Feed intake is usually the first response that is impacted by an inadequate AA supply. Valine and tryptophan imbalances may act as signals for decreasing feed intake. AA are also important nutrients for maintaining the animal's defence systems. Threonine, one of the main constituents of mucin protein, is important for gut development during the postnatal period. It may exert a protective effect that reduces the impact of weaning on gut morphology and associated disturbances. Finally, tryptophan is involved in the regulation of the defence system through its action as a precursor of antioxidants and its effect on the inflammatory response.

Leucine is essential for attenuating fetal growth restriction caused by a protein-restricted diet in rats

Certain amino acids, such as leucine (Leu) are not only substrates for protein synthesis but also are important regulators of protein metabolism. Moreover, it is known that alterations in intrauterine growth favor the development of chronic diseases in adulthood. Therefore, we investigated the role of Leu in combination with other BCAA on effects that are induced by maternal protein restriction on fetal growth. Wistar rats were divided into 4 groups according to the diet provided during pregnancy: control (C; 20% casein); V+I [5% casein + 2% L-valine (Val) + 2% L-isoleucine (Ile)]; KYT [5% casein + 1.8% L-lysine (Lys) + 1.2% L-tyrosine (Tyr) + 1% L-threonine (Thr)]; and BCAA (5% casein + 1.8% L-Leu + 1.2% L-Val + 1% L-Ile). Maternal protein restriction reduced the growth and organ weight of the offspring of dams receiving the V+I and KYT diets compared with the C group. Supplementation with BCAA reversed this growth deficit, minimizing the difference or restoring the mass of organs and carcass fat, the liver and muscle protein, and the RNA concentrations compared with newborns in the C group (P < 0.05). These effects could be explained by the activation of the mTOR signaling pathway, because phosphorylation of 4E-BP1 in the liver of offspring of the BCAA group was greater than that in the C, V+I, and KYT groups. The present results identify a critical role for Leu in association with other BCAA in the activation of the mTOR signaling pathway for the control of altered intrauterine growth induced by a maternal low-protein diet.

Enteral leucine supplementation increases protein synthesis in skeletal and cardiac muscles and visceral tissues of neonatal pigs through mTORC1-dependent pathways

INTRODUCTION

Leucine (Leu) activates mammalian target of rapamycin (mTOR) to upregulate protein synthesis (PS).

RESULTS

PS in skeletal muscles, heart, liver, pancreas, and jejunum, but not kidney, were greater in low protein supplemented with Leu (LP+L) than LP, but lower than high protein (HP). In longissimus dorsi muscle, protein kinase B phosphorylation was similar in LP and LP+L, but lower than HP. Although less than HP, p70 ribosomal S6 kinase 1 (S6K1) and eukaryotic initiation factor (eIF) 4E binding protein 1 (4EBP1) association with regulatory associated protein of mammalian target of rapamycin was greater in LP+L than LP, resulting in higher S6K1 and 4EBP1 phosphorylation. Feeding LP+L vs. LP decreased 4EBP1·eIF4E and increased eIF4E·eIF4G formation, but not to HP. Similar results were obtained for S6K1 and 4EBP1 phosphorylation in gastrocnemius, masseter, heart, liver, pancreas, and jejunum, but not kidney. eIF2α and elongation factor 2 phosphorylation was unaffected by treatment. DICUSSION: Our results suggest that enteral Leu supplementation of a low protein diet enhances PS in most tissues through mTOR complex 1 pathways.

METHODS

To examine enteral Leu effects on PS and signaling activation, 5-d-old piglets were fed for 24 h diets containing: (i) LP, (ii) LP+L, or (iii) HP.

Comparison of high-protein diets and leucine supplementation in the prevention of metabolic syndrome and related disorders in mice

High-protein diets have been shown to promote weight loss, to improve glucose homeostasis and to increase energy expenditure and fat oxidation. We aimed to study whether leucine supplementation is able to mimic the alleviating effects of high-protein diets on metabolic syndrome parameters in mice fed high-fat diet. Male C57BL/6 mice were fed for 20 weeks with semisynthetic high-fat diets (20% w/w of fat) containing either an adequate (10% protein, AP) or high (50% protein, HP) amount of whey protein, or an AP diet supplemented with L-leucine corresponding to the leucine content of the HP diet (6% leucine, AP+L). Body weight and composition, energy expenditure, glucose tolerance, hepatic triacylglycerols (TG), plasma parameters as well as expression levels of mRNA and proteins in different tissues were measured. HP feeding resulted in decreased body weight, body fat and hepatic TG accumulation, as well as increased insulin sensitivity compared to AP. This was linked to an increased total and resting energy expenditure (REE), decreased feed energy efficiency, increased skeletal muscle (SM) protein synthesis, reduced hepatic lipogenesis and increased white fat lipolysis. Leucine supplementation had effects that were intermediate between HP and AP with regard to body composition, liver TG content, insulin sensitivity, REE and feed energy efficiency, and similar effects as HP on SM protein synthesis. However, neither HP nor AP+L showed an activation of the mammalian target of rapamycin pathway in SM. Leucine supplementation had no effect on liver lipogenesis and white fat lipolysis compared to AP. It is concluded that the essential amino acid leucine is able to mimic part but not all beneficial metabolic effects of HP diets.

Skeletal muscle responses to negative energy balance: effects of dietary protein

Sustained periods of negative energy balance decrease body mass due to losses of both fat and skeletal muscle mass. Decreases in skeletal muscle mass are associated with a myriad of negative consequences, including suppressed basal metabolic rate, decreased protein turnover, decreased physical performance, and increased risk of injury. Decreases in skeletal muscle mass in response to negative energy balance are due to imbalanced rates of muscle protein synthesis and degradation. However, the underlying physiological mechanisms contributing to the loss of skeletal muscle during energy deprivation are not well described. Recent studies have demonstrated that consuming dietary protein at levels above the current recommended dietary allowance (0.8 g · kg(-1) · d(-1)) may attenuate the loss of skeletal muscle mass by affecting the intracellular regulation of muscle anabolism and proteolysis. However, the specific mechanism by which increased dietary protein spares skeletal muscle through enhanced molecular control of muscle protein metabolism has not been elucidated. This article reviews the available literature related to the effects of negative energy balance on skeletal muscle mass, highlighting investigations that assessed the influence of varying levels of dietary protein on skeletal muscle protein metabolism. Further, the molecular mechanisms that may contribute to the regulation of skeletal muscle mass in response to negative energy balance and alterations in dietary protein level are described.

Late evening snack: exploiting a period of anabolic opportunity in cirrhosis

BACKGROUND AND AIM

Cirrhosis is a state of accelerated starvation with impaired protein synthesis. Increased rate of gluconeogenesis and alterations in skeletal muscle signaling pathways result in anabolic resistance and consequent loss of muscle mass or sarcopenia in cirrhosis. Late evening snack (LES) is an intervention to reduce the postabsorptive (fasting) phase with the potential to improve substrate utilization and reverse sarcopenia. Published reports were evaluated to examine the effect of LES on regulation of substrate utilization (short-term studies) and nutritional outcomes (long-term studies).

METHODS

PubMed, EMBASE, Google scholar and OVID databases were searched. All studies published on LES in cirrhosis were included. Studies that included few (n < 3) subjects and patients with hepatocellular carcinoma were excluded.

RESULTS

Late evening snack decreased lipid oxidation and improved nitrogen balance, irrespective of the composition or type of formulation used. Daytime isocaloric isonitrogenous snacks did not have the metabolic or clinical benefit of LES. LES decreased skeletal muscle proteolysis. No studies have examined its effect on muscle protein synthesis. There was inconsistent translation into an increase in lean body or skeletal muscle mass. Improved quality of life occurs but decreased mortality or need for transplantation has not been reported. The optimal composition of LES has not been defined, but based on mechanistic considerations, a branched chain supplemented LES holds most promise.

CONCLUSIONS

Late evening snack holds the most promise as an intervention to reverse anabolic resistance and sarcopenia of cirrhosis with improved quality of life in patients with cirrhosis. Long term benefit and improved survival need critical evaluation.

Dietary l-arginine supplementation improves the intestinal development through increasing mucosal Akt and mammalian target of rapamycin signals in intra-uterine growth retarded piglets

Intra-uterine growth retardation (IUGR) impairs postnatal growth and development of the small intestine (SI) in neonatal pigs and infants. l-Arginine (Arg), a critical amino acid involved in promoting growth and metabolism in young mammals, is more deficient in IUGR fetuses. However, little is known whether dietary Arg supplementation would accelerate the impaired development of the SI induced by IUGR in piglets. In the present study, a total of six litters of newborn piglets were used. In each litter, one normal and two IUGR littermates were obtained. Piglets were fed milk-based diets supplemented with 0 (Normal), 0 (IUGR) and 0·60% Arg (IUGR+Arg) from 7 to 14 d of age, respectively. Compared with Normal piglets at 14 d of age, IUGR decreased (P < 0·05) the growth performance, entire SI weight, and villus height in the jejunum and ileum. IUGR piglets had lower (P < 0·05) mucosal concentrations of Arg, insulin, insulin growth factor 1, as well as phosphorylated Akt, mammalian target of rapamycin (mTOR) and p70 S6 kinase but higher (P < 0·05) enterocyte apoptosis index (AI). After Arg treatment in IUGR piglets, the growth performance, weight of entire SI and mucosa, and villus height in the jejunum and ileum were increased (P < 0·05). Diet supplemented with Arg also increased (P < 0·05) the levels of Arg, insulin, phosphorylated Akt and mTOR in SI mucosa of IUGR piglets, and decreased (P < 0·05) the AI and caspase-3 activity. In conclusion, Arg has a beneficiary effect in improving the impaired SI development in IUGR piglets via regulating cell apoptosis and activating Akt and mTOR signals in SI mucosa.

Molecular characterization and functional analysis of Cashmere goat mammalian target of rapamycin

The mammalian target of rapamycin (mTOR) is an evolutionarily conserved protein kinase that belongs to the phosphatidylinositol kinase-related kinase family. We describe our molecular characterization of mTOR and its function (GenBank accession HM114224) in Cashmere goat (Capra hircus). The goat mTOR complementary DNA is 8617 bp, comprising an open reading frame of 7650 bp--corresponding to a polypeptide of 2549 amino acids--and a 909 bp 3' untranslated region with a polyA tract and a polyadenylation signal at nucleotides 8575-8580. In a bioinformatics analysis, goat mTOR has typical sites of activity and domains. mTOR mRNA was measured in brain, heart, testis, liver, spleen, kidney, and lung by real-time polymerase chain reaction, and the expression of mTOR in fetal fibroblasts was detected by western blot. The viability of fetal fibroblasts was inhibited on treatment with CCI-779, a specific inhibitor of mTOR. Our data supplied evidence that the transcription of mTOR was detected in the seven tissues in Cashmere goat, and mTOR protein was translated in fetal fibroblasts. The proliferation of fetal fibroblasts decreases on inhibition of mTOR.

Effect of a Herbal-Leucine mix on the IL-1β-induced cartilage degradation and inflammatory gene expression in human chondrocytes

Background

Conventional treatments for the articular diseases are often effective for symptom relief, but can also cause significant side effects and do not slow the progression of the disease. Several natural substances have been shown to be effective at relieving the symptoms of osteoarthritis (OA), and preliminary evidence suggests that some of these compounds may exert a favorable influence on the course of the disease. The objective of this study was to investigate the anti-inflammatory/chondroprotective potential of a Herbal and amino acid mixture containing extract of the Uncaria tomentosa, Boswellia spp., Lepidium meyenii and L-Leucine on the IL-1β-induced production of nitric oxide (NO), glycosaminoglycan (GAG), matrix metalloproteinases (MMPs), aggrecan (ACAN) and type II collagen (COL2A1) in human OA chondrocytes and OA cartilage explants.

Methods

Primary OA chondrocytes or OA cartilage explants were pretreated with Herbal-Leucine mixture (HLM, 1-10 μg/ml) and then stimulated with IL-1β (5 ng/ml). Effect of HLM on IL-1β-induced gene expression of iNOS, MMP-9, MMP-13, ACAN and COL2A1 was verified by real time-PCR. Estimation of NO and GAG release in culture supernatant was done using commercially available kits.

Results

HLM tested in these in vitro studies was found to be an effective anti-inflammatory agent, as evidenced by strong inhibition of iNOS, MMP-9 and MMP-13 expression and NO production in IL-1β-stimulated OA chondrocytes (p < 0.05). Supporting these gene expression results, IL-1β-induced cartilage matrix breakdown, as evidenced by GAG release from cartilage explants, was also significantly blocked (p < 0.05). Moreover, in the presence of herbal-Leucine mixture (HLM) up-regulation of ACAN and COL2A1 expression in IL-1β-stimulated OA chondrocytes was also noted (p < 0.05). The inhibitory effects of HLM were mediated by inhibiting the activation of nuclear factor (NF)-kB in human OA chondrocytes in presence of IL-1β.

Conclusion

Our data suggests that HLM could be chondroprotective and anti-inflammatory agent in arthritis, switching chondrocyte gene expression from catabolic direction towards anabolic and regenerative, and consequently this approach may be potentially useful as a new adjunct therapeutic/preventive agent for OA or injury recovery.

Influence of leucine on protein metabolism, phosphokinase expression, and cell proliferation in human duodenum1,3

BACKGROUND

Although leucine increases protein anabolism through the mammalian target of rapamycin (mTOR) pathway in human muscles, its effects on intestinal mucosal proteins remain unknown.

OBJECTIVE

We aimed to assess the effects of leucine on duodenal protein metabolism in healthy humans and to elucidate the signaling pathways involved.

DESIGN

Eleven healthy volunteers received for 5 h, on 2 occasions and in random order, an enteral supply of maltodextrins (0.25 g . kg(-1) . h(-1)) or maltodextrins and leucine (0.035 g . kg(-1) . h(-1)) simultaneously with a continuous intravenous infusion of [(2)H(5)]phenylalanine (9 μmol . kg(-1) .h(-1)). Endoscopic duodenal biopsy samples were collected and frozen until analyzed. Phenylalanine enrichment was assessed by gas chromatography-mass spectrometry in duodenal protein and in free intracellular amino acid pools used as precursor to calculate the mucosal fractional synthesis rate (FSR). Proteasome proteolytic activities and phosphokinase expression were assessed by using specific fluorogenic substrates or macroarrays, respectively.

RESULTS

Leucine supplementation slightly reduced FSR (mean ± SEM: 81.3 ± 6.3%/d) compared with maltodextrins alone (91.7 ± 8.5%/d; P = 0.0537). In addition, total proteasome activity decreased significantly with leucine (236 ± 21 compared with 400 ± 58 relative fluorescence units/μg protein; P < 0.05), with no modification of chymotrypsin-like, trypsin-like, caspase-like, or peptidase activities. Leucine did not affect the mTOR pathway but did increase the phosphorylation states of PI3K, Akt, AMPK, p38 MAPK, JNK, GSK-3α/β, STAT3, and STAT5 and increased cyclin D1 mRNA concentrations, which suggested that leucine may enhance cell proliferation.

CONCLUSION

Enteral leucine supplementation decreased proteasome activity in duodenal mucosa and enhanced cell proliferation through the PI3K/Akt/GSK-3α/β-catenin pathway. This trial was registered at clinicaltrials.gov as NCT01254110.

Dietary whey protein lowers the risk for metabolic disease in mice fed a high-fat diet

Consuming a high-fat (HF) diet produces excessive weight gain, adiposity, and metabolic complications associated with risk for developing type 2 diabetes and fatty liver disease. This study evaluated the influence of whey protein isolate (WPI) on systemic energy balance and metabolic changes in mice fed a HF diet. Female C57BL/6J mice received for 11 wk a HF diet, with or without 100 g WPI/L drinking water. Energy consumption and glucose and lipid metabolism were examined. WPI mice had lower rates of body weight gain and percent body fat and greater lean body mass, although energy consumption was unchanged. These results were consistent with WPI mice having higher basal metabolic rates, respiratory quotients, and hepatic mitochondrial respiration. Health implications for WPI were reflected in early biomarkers for fatty liver disease and type 2 diabetes. Livers from WPI mice had significantly fewer hepatic lipid droplet numbers and less deposition of nonpolar lipids. Furthermore, WPI improved glucose tolerance and insulin sensitivity. We conclude that in mice receiving a HF diet, consumption of WPI results in higher basal metabolic rates and altered metabolism of dietary lipids. Because WPI mice had less hepatosteatosis and insulin resistance, WPI dietary supplements may be effective in slowing the development of fatty liver disease and type 2 diabetes.

The biochemical and cellular basis for nutraceutical strategies to attenuate neurodegeneration in Parkinson's disease

Future therapeutic intervention that could effectively decelerate the rate of degeneration within the substantia nigra pars compacta (SNc) could add years of mobility and reduce morbidity associated with Parkinson’s disease (PD). Neurodegenerative decline associated with PD is distinguished by extensive damage to SNc dopaminergic (DAergic) neurons and decay of the striatal tract. While genetic mutations or environmental toxins can precipitate pathology, progressive degenerative succession involves a gradual decline in DA neurotransmission/synaptic uptake, impaired oxidative glucose consumption, a rise in striatal lactate and chronic inflammation. Nutraceuticals play a fundamental role in energy metabolism and signaling transduction pathways that control neurotransmission and inflammation. However, the use of nutritional supplements to slow the progression of PD has met with considerable challenge and has thus far proven unsuccessful. This review re-examines precipitating factors and insults involved in PD and how nutraceuticals can affect each of these biological targets. Discussed are disease dynamics (Sections 1 and 2) and natural substances, vitamins and minerals that could impact disease processes (Section 3). Topics include nutritional influences on α-synuclein aggregation, ubiquitin proteasome function, mTOR signaling/lysosomal-autophagy, energy failure, faulty catecholamine trafficking, DA oxidation, synthesis of toxic DA-quinones, o-semiquinones, benzothiazolines, hyperhomocyseinemia, methylation, inflammation and irreversible oxidation of neuromelanin. In summary, it is clear that future research will be required to consider the multi-faceted nature of this disease and re-examine how and why the use of nutritional multi-vitamin-mineral and plant-based combinations could be used to slow the progression of PD, if possible.