Dietary l-leucine supplementation enhances intestinal development in suckling piglets

Metabolomic and lipidomic insights into the impact of Euglena gracilis-derived β-glucan supplementation on sow colostrum and milk composition

Euglena gracilis, an algae-derived source of β-glucan, exhibits prebiotic activity that enhances colostrum quality and improves growth, though the underlying mechanisms remain unclear. This study investigates the effects of E. gracilis supplementation during late gestation and lactation on sow colostrum and milk biomolecular profiles. Sixty-one crossbred sows (Landrace × Yorkshire) were assigned to a standard diet (CON; n = 30) or the CON diet supplemented with 1 g/sow/day of E. gracilis (TRT; n = 31) from day 85 of gestation until day 21 of lactation. Sow performance, including litter size and weight, was recorded from birth to day 21 of age. Colostrum samples (n = 20; 10 sows/group) were collected within 1 h of farrowing, and milk samples were collected from the same sows on days 3 and 10 of lactation to assess alterations in non-volatile polar metabolites (NVM), fatty acids (FA), and associated metabolic pathways. On average, the litter size at birth was 14.2 ± 2.5 piglets/litter, with no effect of dietary treatment from birth to day 21 of lactation (P > 0.05). However, piglets suckled by TRT sows tended to have higher average daily gain from birth to day 21 of age than those suckled CON sows (191.0 ± 6.7 vs. 173.6 ± 6.8 g/day, P = 0.073). Chemometric analysis revealed distinct NVM and FA profiles between the groups, particularly in the colostrum. Although E. gracilis supplementation influenced the contents of multiple metabolites, focus has been given to those that have direct impact on piglet development, including increased colostrum leucine (P = 0.001), threonine (P < 0.001), and N-acetylglucosamine (P = 0.002), enhancing colostrum quality and immunomodulatory potential. Elevated colostrum gamma-linolenic acid (P = 0.047) and arachidonic acid (P = 0.019) levels suggested enhanced immune development. Pathways associated with amino sugars and nucleotide sugars and glucose-related metabolism in colostrum were also modulated. These findings suggest E. gracilis-derived β-glucan as a potential dietary supplement for enhancing sow colostrum quality and piglet growth.

L-leucine promotes the synthesis of milk protein and milk fat in bovine mammary epithelial cells through the AKT/mTOR signaling pathway under hypoxic conditions

Hypoxia stress has been demonstrated to impede animal embryonic development, spermatogenesis, and lactation, leading to decreased animal production performance. However, the impact of hypoxia-induced activation of hypoxia inducible factor-1 (HIF-1) signaling on milk protein and fat synthesis remains unclear. L-leucine, a branched-chain amino acid, is known to modulate milk protein and fat synthesis. Therefore, our study aimed to evaluate the effect of L-leucine on milk protein and fat synthesis under hypoxic conditions and shed light on the molecular mechanism using an in vitro model. The results indicated that hypoxia treatment significantly decreased the synthesis of α-casein and β-casein, as well as inhibited factors related to milk fat synthesis in bovine mammary epithelial cells (MAC-T). Additionally, hypoxia stress suppressed the activities of the mammalian target of rapamycin (mTOR) and protein kinase B (AKT). Interfering with HIF-1α significantly reversed the expression of AKT, mTOR and factors related to milk synthesis. Importantly, supplementation with L-leucine activated AKT/mTOR signaling, thereby enhancing milk protein and fat synthesis in MAC-T cells to some extent. In conclusion, these findings suggest that HIF-1 signaling plays an important role in milk synthesis and that L-leucine may stimulate the synthesis of milk protein and fat by activating the AKT/mTOR signaling pathway under hypoxic conditions, making it a potential additive for promoting milk synthesis inhibited by hypoxia.

High-level L-Gln compromises intestinal amino acid utilization efficiency and inhibits protein synthesis by GCN2/eIF2α/ATF4 signaling pathway in piglets fed low-crude protein diets

Gln, one of the most abundant amino acids (AA) in the body, performs a diverse range of fundamental physiological functions. However, information about the role of dietary Gln on AA levels, transporters, protein synthesis, and underlying mechanisms in vivo is scarce. The present study aimed to explore the effects of low-crude protein diet inclusion with differential doses of L-Gln on intestinal AA levels, transporters, protein synthesis, and potential mechanisms in weaned piglets. A total of 128 healthy weaned piglets (Landrace × Yorkshire) were randomly allocated into four treatments with four replicates. Pigs in the four groups were fed a low-crude protein diet containing 0%, 1%, 2%, or 3% L-Gln for 28 d. L-Gln administration markedly (linear, P < 0.05) increased Ala, Arg, Asn, Asp, Glu, Gln, His, Ile, Lys, Met, Orn, Phe, Ser, Thr, Tyr, and Val levels and promoted trypsin activity in the jejunal content of piglets. Moreover, L-Gln treatment significantly enhanced concentrations of colonic Gln and Trp, and serum Thr (linear, P < 0.01), and quadratically increased serum Lys and Phe levels (P < 0.05), and decreased plasma Glu, Ile, and Leu levels (linear, P < 0.05). Further investigation revealed that L-Gln administration significantly upregulated Atp1a1, Slc1a5, Slc3a2, Slc6a14, Slc7a5, Slc7a7, and Slc38a1 relative expressions in the jejunum (linear, P < 0.05). Additionally, dietary supplementation with L-Gln enhanced protein abundance of general control nonderepressible 2 (GCN2, P = 0.010), phosphorylated eukaryotic initiation factor 2 subunit alpha (eIF2α, P < 0.001), and activating transcription factor 4 (ATF4) in the jejunum of piglets (P = 0.008). These results demonstrated for the first time that a low crude protein diet with high-level L-Gln inclusion exhibited side effects on piglets. Specifically, 2% and 3% L-Gln administration exceeded the intestinal utilization capacity and compromised the jejunal AA utilization efficiency, which is independent of digestive enzyme activities. A high level of L-Gln supplementation would inhibit protein synthesis by GCN2/eIF2α/ATF4 signaling in piglets fed low-protein diets, which, in turn, upregulates certain AA transporters to maintain AA homeostasis.

Regulation of Isoleucine on Colonic Barrier Function in Rotavirus-Infected Weanling Piglets and Analysis of Gut Microbiota and Metabolomics

Rotavirus (RV) is a significant contributor to diarrhea in both young children and animals, especially in piglets, resulting in considerable economic impacts on the global pig industry. Isoleucine (Ile), a branched-chain amino acid, is crucial for regulating nutrient metabolism and has been found to help mitigate diarrhea. This study aimed to assess the impact of isoleucine supplementation in feed on colonic barrier function, colonic microbiota, and metabolism in RV-infected weanling piglets. A total of thirty-two weaned piglets, aged 21 days, were randomly assigned to two dietary groups (each further divided into two subgroups, with eight replicates in each subgroup), receiving diets with either 0% or 1% isoleucine for a duration of 14 days. One group from each treatment was then challenged with RV, and the experimental period lasted for 19 days. The results showed that dietary Ile significantly increased the secretion of IL-4, IL-10, and sIgA in the colon of RV-infected weanling piglets (p < 0.05). In addition, Ile supplementation notably increased the expression of tight junction proteins, including Claudin-3, Occludin, and ZO-1 (p < 0.01), as well as the mucin protein MUC-1 in the colon of RV-infected weanling piglets (p < 0.05). Gut microbiota analysis revealed that dietary Ile increased the relative abundance of Prevotella and decreased the relative abundance of Rikenellaceae in the colons of RV-infected weanling piglets. Compared with the RV+CON, metabolic pathways in the RV+ILE group were significantly enriched in vitamin digestion and absorption, steroid biosynthesis, purine metabolism, pantothenate and CoA biosynthesis, cutin, suberine, and wax biosynthesis, as well as fatty acid biosynthesis, and unsaturated fatty acid biosynthesis. In conclusion, dietary Ile supplementation can improve immunity, colonic barrier function, colonic microbiota, and colonic metabolism of RV-infected weaned piglets. These findings provide valuable insights into the role of isoleucine in the prevention and control of RV.

Impacts of Maternal Nutrition on Sow Performance and Potential Positive Effects on Piglet Performance

The objectives of this review are to identify the nutritional challenges faced by modern sows and present potential solutions to mitigate excessive maternal tissue loss and reproductive failure as it relates to recent genetic improvements. Current feeding programs have limitations to support the rapid genetic improvements in reproductive performance for modern sows. Since 2012, both litter size at birth and fetal weight have increased by 2.26 pigs per litter and 0.22 kg per piglet, respectively, thereby increasing the nutrient needs for sows during gestation and lactation. Prediction models generated in this review predict that modern sows would need 31% more lysine during gestation when compared with current feeding programs. Physiological challenges facing modern sows are also addressed in this review. High oxidative stress, pelvic organ prolapse, and lameness can directly affect the sow, whereas these physiological challenges can have negative impacts on colostrum and milk quality. In response, there is growing interest in investigating the functional roles of select bioactive compounds as feed additives to mitigate the severity of these challenges. Selenium sources, catechins, and select plant extracts have been utilized to reduce oxidative stress, calcium chloride and phytase have been used to mitigate pelvic organ prolapse and lameness, algae and yeast derivatives have been used to improve colostrum and milk quality, and fiber sources and probiotics have been commonly utilized to improve sow intestinal health. Collectively, this review demonstrates the unique challenges associated with managing the feeding programs for modern sows and the opportunities for revision of the amino acid requirements as well as the use of select bioactive compounds to improve reproductive performance.

Leucine regulates lipid metabolism in adipose tissue through adipokine-mTOR-SIRT1 signaling pathway and bile acid-microbe axis in a finishing pig model

This study was conducted to explore the regulatory mechanism of leucine (Leu) on lipid metabolism of finishing pigs. Twenty-four Duroc × Landrace × Large cross pigs with an average body weight of 68.33 ± 0.97 kg were randomly allocated into 3 treatment groups with 8 replicates per group (1 pig per replicate). The dietary treatments were as follows: control group (CON), 0.25% Leu group and 0.50% Leu group. The experimental period was 42 d. The results showed as follows. (1) Compared with the CON, 0.25% and 0.50% Leu increased (P < 0.01) the average daily gain (ADG), while the average backfat thickness (ABT) and the ratio of feed intake to body weight gain (F:G ratio) were decreased (P < 0.05). (2) In the 0.25% Leu group, the relative mRNA expression levels of sterol regulatory element binding protein-1c (SREBP1c), recombinant fatty acid transport protein 1 (FATP1), chemerin and peroxisome proliferator-activated receptor γ (PPARγ) were decreased but the level of fatty acid binding protein 4 (FABP4) and fatty acid translocase (FAT/CD36) were increased in backfat tissue. In the 0.25% Leu group, the protein levels of p-Rictor, p-Raptor, p-eIF4E-binding protein 1 (p-4EBP1), p-silent mating type information regulator 2 homolog 1 (p-SIRT1) and acetylation ribosome s6 protein kinase 1 (Ac-S6K1) were increased (P < 0.05). (3) Compared to the CON, the diversity of gut microbiota in the 0.25% Leu group was increased. Principal component analysis showed that the relative abundance of Bacteroidetes, Lactobacillus and Desulfovibrio was higher in the 0.25% Leu group than the CON, but the relative abundance of Firmicutes, Treponema and Shigella was lower than in the CON (P < 0.05). (4) Four different metabolites were screened out from the serum of finishing pigs including allolithocholic acid (alloLCA), isolithocholic acid (isoLCA), ursodeoxycholic acid (UDCA) and hyodeoxycholic acid (HDCA), which correlate to various degrees with the above microorganisms. In conclusion, Leu could promote adipose tissue lipolysis of finishing pigs through the mTOR-SIRT1 signaling pathway, and S6K1 is acetylated at the same time, and the interaction between gut microbiota and bile acid metabolism is also involved.

Amino acids in piglet diarrhea: Effects, mechanisms and insights

Piglet diarrhea is among one of the most serious health problems faced by the pig industry, resulting in significant economic losses. Diarrheal disease in piglets has a multifactorial etiology that is affected by physiology, environment, and management strategy. Diarrhea is the most apparent symptom of intestinal dysfunction. As a key class of essential nutrients in the piglet diet, amino acids confer a variety of beneficial effects on piglets in addition to being used as a substrate for protein synthesis, including maintaining appropriate intestinal integrity, permeability and epithelial renewal, and alleviating morphological damage and inflammatory and oxidative stress. Thus, provision of appropriate levels of amino acids could alleviate piglet diarrhea. Most amino acid effects are mediated by metabolites, gut microbes, and related signaling pathways. In this review, we summarize the current understanding of dietary amino acid effects on gut health and diarrhea incidence in piglets, and reveal the mechanisms involved. We also provide ideas for using amino acid blends and emphasize the importance of amino acid balance in the diet to prevent diarrhea in piglets.

Branched-chain amino acid supplementation does not enhance lean tissue accretion in low birth weight neonatal pigs, despite lower Sestrin2 expression in skeletal muscle

Postnatal muscle growth is impaired in low birth weight (L) neonatal pigs. Leucine supplementation has been established as a dietary intervention to enhance muscle growth in growing animals. The aim of this study was to investigate the efficacy of supplementing L neonatal pig formulas with branched-chain amino acids (B) to enhance the rate of protein accretion. Twenty-four 3-day old pigs were divided into two groups low (L) and normal birth weight (N) based on weight at birth. Pigs were assigned to a control (C) or 1% branched-chain amino acids (B) formulas, and fed at 250 mL·kg body weight -1·d-1 for 28 d. Body weight of pigs in the L group was less than those in the N group (P < 0.01). However, fractional body weight was greater for L pigs compared with their N siblings from day 24 to 28 of feeding regardless of formula (P < 0.01). In addition, feed efficiency (P < 0.0001) and efficiently of protein accretion (P < 0.0001) were greater for L than N pigs regardless of supplementation. Pigs fed the B formula had greater plasma leucine, isoleucine, and valine concentrations compared with those fed the C formula (P < 0.05). Longissimus dorsi Sestrin2 protein expression was less for pigs in the L group compared with those in the N group (P < 0.01), but did not result in a corresponding increase in translation initiation signaling. Longissimus dorsi mRNA expression of BCAT2 was less for LB pigs compared with those in the LC group, and was intermediate for NC and NB pigs (P < 0.05). Hepatic mRNA expression of BCKDHA was greater for pigs in the L compared with those in the N groups (P < 0.05). However, plasma branched-chain keto-acid concentration was reduced for C compared with those in the B group (P < 0.05). These data suggest that branched-chain amino acid supplementation does not improve lean tissue accretion of low and normal birth weight pigs, despite a reduction in Sestrin2 expression in skeletal muscle of low birth weight pigs. The modest improvement in fractional growth rate of low birth weight pigs compared with their normal birth weight siblings was likely due to a more efficient dietary protein utilization.

Comprehensive study on the effect of dietary leucine supplementation on intestinal physiology, TOR signaling and microbiota in juvenile turbot (Scophthalmus maximus L.)

Intestinal damage and inflammation are major health and welfare issues in aquaculture. Considerable efforts have been devoted to enhancing intestinal health, with a specific emphasis on dietary additives. Branch chain amino acids, particularly leucine, have been reported to enhance growth performance in various studies. However, few studies have focused on the effect of leucine on the intestinal function and its underlying molecular mechanism is far from fully illuminated. In the present study, we comprehensively evaluated the effect of dietary leucine supplementation on intestinal physiology, signaling transduction and microbiota in fish. Juvenile turbot (Scophthalmus maximus L.) (10.13 ± 0.01g) were fed with control diet (Con diet) and leucine supplementation diet (Leu diet) for 10 weeks. The findings revealed significant improvements in intestinal morphology and function in the turbot fed with Leu diet. Leucine supplementation also resulted in a significant increase in mRNA expression levels of mucosal barrier genes, indicating enhanced intestinal integrity. The transcriptional levels of pro-inflammatory factors il-1β, tnf-α and irf-1 was decreased in response to leucine supplementation. Conversely, the level of anti-inflammatory factors tgf-β, il-10 and nf-κb were up-regulated by leucine supplementation. Dietary leucine supplementation led to an increase in intestinal complement (C3 and C4) and immunoglobulin M (IgM) levels, along with elevated antioxidant activity. Moreover, dietary leucine supplementation significantly enhanced the postprandial phosphorylation level of the target of rapamycin (TOR) signaling pathway in the intestine. Finally, intestinal bacterial richness and diversity were modified and intestinal bacterial composition was re-shaped by leucine supplementation. Overall, these results provide new insights into the beneficial role of leucine supplementation in promoting intestinal health in turbot, offering potential implications for the use of leucine as a nutritional supplement in aquaculture practices.

Limosilactobacillus mucosae and Lactobacillus amylovorus Protect Against Experimental Colitis via Upregulation of Colonic 5-Hydroxytryptamine Receptor 4 and Transforming Growth Factor-β2

BACKGROUND

Limosilactobacillusmucosae (LM) exerts anti-inflammatory and health-promoting effects. However, its role in the modulation of gut serotonin or 5-hydroxytryptamine (5-HT) metabolism and 5-HT receptors (HTRs) in inflammation requires further investigation.

OBJECTIVES

We compared LM with Lactobacillus amylovorus (LA) for the regulation of 5-HT, HTRs, inflammatory mediators, and their correlations in the colon of mice with experimental colitis.

METHODS

Male C57BL/6 mice were randomly assigned to 6 groups: control (Con), LM, LA, dextran sodium sulfate (DSS), and DSS with pre-administration of LM (+LM) or LA (+LA). After 7 d of DSS treatment, mice were killed to analyze the expression of inflammatory mediators, HTRs, and concentrations of 5-HT and microbial metabolites in the colon.

RESULTS

LM was more effective than LA in alleviating DSS-induced colonic inflammation. Compared with mice in the DSS group, mice receiving DSS + LM or DSS + LA treatment had lower (P < 0.05) colonic mRNA expression of proinflammatory cytokines. DSS + LM treatment had lower mRNA expression of Il1b, Tnfa, and Ccl3, an abundance of p-STAT3, and greater expression of Tgfb2 and Htr4 in the colon (P < 0.05). The expression of inflammatory mediators (including Tgfb-1) was positively correlated (P < 0.05) with 5-HT and Htr2a and negatively correlated (P < 0.05) with Htr4. However, the expression of Tgfb-2 showed reversed correlations with the 5-HT and HTRs described above. Patterns for these correlations were different for LM and LA. Mice receiving the DSS + LM treatment had greater (P < 0.05) concentrations of acetate and valerate and lower (P < 0.05) concentrations of indole-3-acetic acid in the cecal and colonic contents.

CONCLUSIONS

LM showed greater efficacy than LA in alleviating DSS-induced colonic inflammation. The coordinated regulation of transforming growth factor-β subtypes and serotonin receptors in the colon may be one of the most important mechanisms underlying the probiotic effects of lactobacilli in gut inflammation.

l-Leucine supplementation reduces growth performance accompanied by changed profiles of plasma amino acids and expression of jejunal amino acid transporters in breast-fed intra-uterine growth-retarded piglets

Previously, we provided an evidence that l-Leucine supplementation facilitates growth performance in suckling piglets with normal birth weight. However, it remains hitherto obscure weather breast-fed piglets displaying intra-uterine growth restriction (IUGR) show a similar effect in response to l-Leucine provision. In this study, 7-d-old sow-reared IUGR piglets were orally administrated with l-Leucine (0, 0·7, 1·4 or 2·1 g/kg BW) twice daily for 2 weeks. Increasing leucine levels hampered the growth performance of suckling IUGR piglets. The average daily gain of IUGR piglets was significantly reduced in 1·4 g/kg BW and 2·1 g/kg BW l-Leucine supplementation groups (P < 0·05). Except for ornithine and glutamine, the plasma concentrations of other amino acids were abated as l-Leucine levels increased (P < 0·05). Leucine supplementation led to reduction in the levels of urea, blood ammonia, blood glucose, TAG and total cholesterol, as well as an elevation in the level of LDL-cholesterol in suckling IUGR piglets (P < 0·05). In addition, 1·4 g/kg BW of l-Leucine enhanced the mRNA expression of ATB0,+, whereas decreased the mRNA abundances of CAT1, y + LAT1, ASCT2 and b0,+AT in the jejunum (P < 0·05). Concomitantly, the jejunum of IUGR piglets in l-Leucine group contains more ATB0,+ and less SNAT2 protein than in the control (P < 0·05). Collectively, l-Leucine supplementation impairs growth performance in breast-fed IUGR piglets, which may be associated with depressed nutritional conditions and alterations in the uptake of amino acids and the expression of amino acid transporters in the small intestine.

Low rumen degradable starch promotes the growth performance of goats by increasing protein synthesis in skeletal muscle via the AMPK-mTOR pathway

Since starch digestion in the small intestine provides more energy than digestion in the rumen of ruminants, reducing dietary rumen degradable starch (RDS) content is beneficial for improving energy utilization of starch in ruminants. The present study tested whether the reduction of rumen degradable starch by restricting dietary corn processing for growing goats could improve growth performance, and further investigated the possible underlying mechanism. In this study, twenty-four 12-wk-old goats were selected and randomly allocated to receive either a high RDS diet (HRDS, crushed corn-based concentrate, the mean of particle sizes of corn grain = 1.64 mm, n = 12) or a low RDS diet (LRDS, non-processed corn-based concentrate, the mean of particle sizes of corn grain >8 mm, n = 12). Growth performance, carcass traits, plasma biochemical indices, gene expression of glucose and amino acid transporters, and protein expression of the AMPK-mTOR pathway were measured. Compared to the HRDS, LRDS tended to increase the average daily gain (ADG, P = 0.054) and decreased the feed-to-gain ratio (F/G, P < 0.05). Furthermore, LRDS increased the net lean tissue rate (P < 0.01), protein content (P < 0.05) and total free amino acids (P < 0.05) in the biceps femoris (BF) muscle of goats. LRDS increased the glucose concentration (P < 0.01), but reduced total amino acid concentration (P < 0.05) and tended to reduce blood urea nitrogen (BUN) concentration (P = 0.062) in plasma of goats. The mRNA expression of insulin receptors (INSR), glucose transporter 4 (GLUT4), L-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (4F2hc) in BF muscle, and sodium-glucose cotransporters 1 (SGLT1) and glucose transporter 2 (GLUT2) in the small intestine were significantly increased (P < 0.05) in LRDS goats. LRDS also led to marked activation of p70-S6 kinase (S6K) (P < 0.05), but lower activation of AMP-activated protein kinase (AMPK) (P < 0.05) and eukaryotic initiation factor 2α (P < 0.01). Our findings suggested that reducing the content of dietary RDS enhanced postruminal starch digestion and increased plasma glucose, thereby improving amino acid utilization and promoting protein synthesis in the skeletal muscle of goats via the AMPK-mTOR pathway. These changes may contribute to improvement in growth performance and carcass traits in LRDS goats.

The Linear-Logistic Model: A Novel Paradigm for Estimating Dietary Amino Acid Requirements

This study aimed to determine whether current methods for estimating AA requirements for animal health and welfare are sufficient. An exploratory data analysis (EDA) was conducted, which involved a review of assumptions underlying AA requirements research, a data mining approach to identify animal responses to dietary AA levels exceeding those for maximum protein retention, and a literature review to assess the physiological relevance of the linear-logistic model developed through the data mining approach. The results showed that AA dietary levels above those for maximum growth resulted in improvements in key physiological responses, and the linear-logistic model depicted the AA level at which growth and protein retention rates were maximized, along with key metabolic functions related to milk yield, litter size, immune response, intestinal permeability, and plasma AA concentrations. The results suggest that current methods based solely on growth and protein retention measurements are insufficient for optimizing key physiological responses associated with health, survival, and reproduction. The linear-logistic model could be used to estimate AA doses that optimize these responses and, potentially, survival rates.

Gut microbiota: A new target for traditional Chinese medicine in the treatment of depression

ETHNIC PHARMACOLOGICAL RELEVANCE

The causes of depression are complex. Many factors are involved in its pathogenesis, including the individual's biological and social environment. Although numerous studies have reported that the gut microbiota plays a significant role in depression, drugs that regulate the gut microbiota to treat depression have not yet been comprehensively reviewed. At the same time, more and more attention has been paid to the characteristics of traditional Chinese medicine (TCM) in improving depression by regulating gut microbiota. In ancient times, fecal microbiota transplantation was recorded in TCM for the treatment of severe diseases. There are also records in Chinese ancient books about the use of TCM to adjust gut microbiota to treat diseases, which has opened up a unique research field in TCM. Therefore, this article focuses on the pharmacological effects, targets, and mechanisms of TCM in improving depression by mediating the influence of gut microbiota.

AIM OF THIS REVIEW

To summarize the role the gut microbiota plays in depression, highlight potential regulatory targets, and elucidate the anti-depression mechanisms of TCMs through regulation of the gut microbiota.

METHODS

A systematic review of 256 clinical trials and pharmaceutical studies published until June 2022 was conducted in eight electronic databases (Web of Science, PubMed, SciFinder, Research Gate, ScienceDirect, Google Scholar, Scopus, and China Knowledge Infrastructure), according to the implemented PRISMA criteria, using the search terms "traditional Chinese medicine," "depression," and "gut microbiota."

RESULTS

Numerous studies reported the effects of different gut bacteria on depression and that antidepressants work through the gut microbiota. TCM preparations based on compound Chinese medicine, the Chinese Materia Medica, and major bioactive components exerted antidepressant-like effects by improving levels of neurotransmitters, short-chain fatty acids, brain-derived neurotrophic factor, kynurenine, and cytokines via regulation of the gut microbiota.

CONCLUSION

This review summarized the anti-depression effects of TCM on the gut microbiota, providing evidence that TCMs are safe and effective in the treatment of depression and may provide a new therapeutic approach.

Excessive dietary L-tryptophan regulated amino acids metabolism and serotonin signaling in the colon of weaning piglets with acetate-induced gut inflammation

L-Tryptophan (Trp) was shown to improve the gut barrier and growth of weaning piglets. However, whether excessive dietary Trp regulates amino acids (AAs) metabolism and gut serotonin (5-HT) homeostasis in piglets with gut inflammation is not clear yet. We hypothesize that excessive dietary Trp alleviates acetate-induced colonic inflammation and gut barrier damage in weaning piglets partially through the regulation of colonic AAs metabolism and 5-HT signaling. Fifty-four 21-day-old weaned piglets were divided into six groups: control, acetate, 0.2%Trp, 0.2%Trp + acetate, 0.4% Trp, and 0.4%Trp + acetate. Piglets were fed a basal diet supplemented with 0%, 0.2%, or 0.4% of Trp throughout the 12-day experiment. During days 0-7, all piglets had free access to diet and drinking water. On day 8, piglets were intrarectal administered with 10 mL of 10% acetate saline solution or 0.9% saline. During days 8-12, all piglets were pair-fed the same amount of feed per kg bodyweight. Results showed that excessive dietary Trp alleviated acetate-induced reductions in daily weight gain and increase in feed/gain ratio. Trp restored (P < 0.05) acetate-induced increase in concentrations of free aspartate, glutamate/glutamine, glycine, 5-HT, and 3-methylindole in the colon, downregulation of zonula occludens-1 and 5-HT reuptake transporter (SERT) expression and upregulation of IL-1β, IL-8, TLR4, and 5-HT receptor 2A (HTR2A) expression, and the increase in ratios of p-STAT3/ STAT3 and p-p65/p65 in the colon. The above findings suggested that excessive dietary Trp in the proper amount regulated colonic AAs metabolism, 5-HT homeostasis, and signaling that may contribute as important regulators of gut inflammation during the weaning transition.

Dietary Isoleucine and Valine: Effects on Lipid Metabolism and Ureagenesis in Pigs Fed with Protein Restricted Diets

A mixture of valine (Val) and isoleucine (Ile) not only decreases the negative impact of very low protein (VLP) diets on the growth of pigs, but also influences the nitrogen (N) balance and lipid metabolism; however, the underlying pathways are not well understood. This study aimed to investigate the effect of dietary Val and Ile on lipogenesis, lipolysis, and ureagenesis under protein restriction. After one week of acclimation, forty three-week-old pigs were randomly assigned to following dietary treatments (n = 8/group) for 5 weeks: positive control (PC): normal protein diet; negative control (NC): VLP diet; HV: NC supplemented with Val; HI: NC supplemented with Ile; and HVI: NC supplemented with both Val and Ile. HVI partially improved the body weight and completely recovered the feed intake (FI) of pigs fed with NC. HVI increased thermal radiation and improved the glucose clearance. HVI had a lower blood triglyceride than PC and blood urea N than NC. NC and HV promoted lipogenesis by increasing the transcript of fatty acid synthase (FAS) in the liver and lipoprotein lipase (LPL) in adipose tissue but reducing hormone-sensitive lipase (HSL) in the liver. HVI reduced the increased rate of lipogenesis induced by the NC group through normalizing the mRNA abundance of hepatic FAS, sterol regulatory element binding transcription factor 1, and HSL and LPL in adipose tissue. NC, HV, HI, and HVI reduced the ureagenesis by decreasing the protein abundance of carbamoyl phosphate synthetase I, ornithine transcarboxylase, and arginosuccinate lyase in the liver. Overall, HVI improved the growth, FI, and glucose clearance, and decreased the rate of lipogenesis induced by VLP diets.

Apparent jejunal amino acid digestibility, gut morphology, and the expression of intestinal amino acid transporters in pigs fed protein or free amino acids

Dietary amino acids (AA) supplied as protein or in free form are not only digested and absorbed at different rates but can also induce differences in the intestinal physiology of pigs. We compared the apparent jejunal AA digestibility, intestinal morphology, and gene expression of AA transporters of pigs fed diets providing different forms of AA. Thirty growing pigs (33.7 ± 4.1 kg) were fed one of three experimental diets that provided AA either as protein from feather meal (INT), as free AA and small peptides obtained by extensive acid hydrolysis of feathers (HYD), or as a mix of individual purified AA with the same AA profile as HYD (FAA). Pigs were fed the same quantity of feed, energy, and AA. After 14 d, pigs were slaughtered 3 h after feeding a meal with indigestible markers. Digesta and tissue were collected from different sections of the small intestine. Jejunal digesta was used to measure apparent jejunal digestibility of AA. Samples of the duodenum, jejunum, and ileum were used to measure intestinal morphology and the gene expression of intestinal AA transporters. The measured apparent jejunal digestibility of AA of INT was lower compared to HYD and FAA (P < 0.05). The apparent jejunal digestibility of Cys, Gly, His, Met, and Pro was lower for FAA compared to HYD (P < 0.05). This may be due to the small peptides in HYD, which are absorbed faster than individual AA. The villi area in the ileum of HYD fed pigs was the highest (P < 0.05) among the treatments, which may be associated with the reabsorption of endogenous proteins, which occurs mostly in the ileum. In the duodenum, HYD and FAA had lower expression of PepT1 (P < 0.01) probably due to the rapid transit time of digesta compared to INT fed pigs. Pigs fed HYD expressed more ASCT2 (P = 0.02) and CAT-1 (P = 0.04) in the jejunum compared to the pigs fed the other diets. The expression of these transporters along the intestine depended on the relative abundance of readily absorbable dietary AA. Results showed that dietary AA form can have an influence on the morphology and on the expression of different AA transporters along the different sections of the small intestine.

Effect of Isoleucine and Added Valine on Performance, Nutrients Digestibility and Gut Microbiota Composition of Pigs Fed with Very Low Protein Diets

Little is known whether a combination Ile and added Val improves the growth of pigs offered very low protein (VLP) diets through changes in nutrients digestibility and gut microbiota. The objective of this study was to investigate the effect of a mixture of Val above and Ile at NRC levels on growth, nutrient digestibility and gut microbiota in pigs fed with VLP diets. Forty, weaned piglets were assigned to: positive control: normal-protein-diet; negative control (NC): VLP diet supplemented with first four limiting amino acids; VA: NC with Val above NRC; IL: NC with Ile at NRC level; VAIL: NC with Val above and Ile at NRC levels. While both VAIL and VA groups completely recovered the inhibitory effects of VLP diets on feed intake, only VAIL partially recovered the negative effects of VLP diets on growth performance. VAIL and VA increased the thermal radiation and decreased the digestibility of nitrogen. NC increased the relative abundance of Pasteurellaceae and Enterobacteriaceae in the colon. VAIL had a higher abundance of colonic Actinobacteria, Enterococcus, and Brevibacillus and the colon content of VA was more enriched with Mogibacterium. Overall, VAIL partially improved the growth performance which is likely linked with alterations in gut microbiota composition.

Suckling Induces Differential Gut Enzyme Activity and Body Composition Compared to Feeding Milk Replacer in Piglets

The aim of this study was to investigate differences in growth, hematology, metabolism, small intestine (SI) morphology, and enzyme activity of sow-reared piglets (SOW) compared to artificially reared piglets (MILK) given milk replacers in two different environments. Thirty-six piglets were selected at birth based on their birth weight; eighteen were kept on a commercial farm, another eighteen transferred to an animal research facility for artificial rearing. Differences were observed in enzymatic activity, with a larger amount of sucrase in the SOW compared with MILK group across the SI. SOW piglets also had a body composition with a larger amount of fat, muscle, and bone mass content. Differences in hematology were observed, suggesting environmental influences, biochemistry differences reflective of the diets given, and finally, an increased dry matter (DM) intake in SOW piglets was estimated. No differences were observed in immune function and only small differences in the gut integrity were found between the two groups. It can be concluded that body composition and enzyme activity can be manipulated through dietary intervention and that an increase in DM during lactation is beneficial for gut function. The study warrants further investigation into what this means for the subsequent weaning period.

Weaning Stress in Piglets Alters the Expression of Intestinal Proteins Involved in Fat Absorption

BACKGROUND

In vivo data on intestinal fat absorption in weanling piglets are scarce.

OBJECTIVES

This study aimed to investigate the effect of weaning stress on intestinal fat absorption.

METHODS

Eighteen 7-d-old sow-reared piglets (Duroc-Landrace-Yorkshire) were assigned to 3 groups (n = 6/group, 3 males and 3 females per group). Piglets were nursed by sows until 24 d of age (suckling piglets, S), or weaned at 21 d of age to a corn-soybean meal-based diet until 24 d (3 d postweaning, W3) or 28 d (7 d postweaning, W7) of age, respectively. Duodenum, jejunum, and ileum were collected to determine intestinal morphology and abundance of proteins related to fat absorption.

RESULTS

Compared with the S group, the W3 group had lower villus height (17-34%) and villus height to crypt depth ratio (13-53%), as well as 1-1.45 times greater crypt depth; these values were 1.18-1.31, 0.69-1.15, and 1.47-1.87 times greater in the W7 group than in the W3 group, respectively. Compared with the S group, weaning stress for both W3 and W7 groups reduced intestinal alkaline phosphatase activity (26-73%), serum lipids (26-54%), and abundances of proteins related to fatty acid transport [fatty acid transport protein 4 (FATP4) and intestinal fatty acid-binding protein (I-FABP)] and chylomicron assembly [microsomal triglyceride transfer protein (MTTP), apolipoprotein A-IV (APOA4), B (APOB), and A-I (APOA1)] in the duodenum and ileum (10-55%), as well as in the jejunum (25-85%). All these indexes did not differ between W3 and W7 groups. Compared with the S group, the W3 group had lower mRNA abundances of duodenal APOA4 and APOA1 (25-50%), as well as jejunal FATP4, IFABP, MTTP, APOA4, and APOA1 (35-50%); these values were 5-15% and 10-37% lower in the W7 group than in the W3 group, respectively.

CONCLUSIONS

Weaning stress in piglets attenuates the expression of intestinal proteins related to fatty acid transport (FATP4 and I-FABP) and chylomicron synthesis (APOA4).

Effects of dietary protein content and crystalline amino acid supplementation patterns on growth performance, intestinal histomorphology, and immune response in weaned pigs raised under different sanitary conditions

The aim of this experiment was to investigate the effects of dietary crude protein (CP) contents and crystalline amino acids (CAA) supplementation patterns on growth performance, intestinal histomorphology, and immune response in weaned pigs under clean (CSC) or unclean sanitary conditions (USC). A total of 144 weaned pigs (6.35 ± 0.63 kg body weight) were assigned to 6 treatments in a 3 × 2 factorial arrangement based on CP content and sanitary conditions using a randomized complete block design, giving 8 replicates per treatment with 3 pigs per pen. Pigs were fed one of three diets for 21 d: one high CP (HCP; 22%) and two low CP (LCP; 19%) diets supplemented with 9 indispensable AA or only 6 AA (Lys, Met, Thr, Trp, Val, and Ile) as CAA. The CSC room was washed weekly, whereas the USC room had sow manure spread in the pens and was not washed throughout the experiment. Body weight and feed disappearance were recorded weekly. Blood was sampled from 1 pig per pen weekly, and the same pig was euthanized for jejunal tissues sampling on day 21. Pigs raised under USC had reduced (P < 0.05) average daily gain (ADG) and gain to feed ratio (G:F) in week 2, but contrary results that greater (P < 0.05) ADG and G:F were found in pigs under USC in week 3. Overall, there was an interaction where G:F did not differ between HCP and LCP under CSC, however, LCP decreased (P < 0.05) G:F compared to HCP under USC. Pigs fed the HCP diet had higher (P < 0.05) fecal scores than those fed the LCP diets throughout the experiment. Pigs fed the LCP had higher (P < 0.05) villus height to crypt depth ratio than those fed the HCP. An interaction was observed where goblet cell density in the jejunum was higher (P < 0.05) in pigs fed LCP than HCP under CSC, but no difference was found between HCP and LCP under USC. Different CAA supplementation patterns did not influence both growth performance and histomorphology. Pigs raised under USC had greater (P < 0.05) plasma interleukin (IL)-10 and IL-6 concentrations and reduced (P < 0.05) plasma tumor necrosis factor-alpha concentration. Also, the LCP diets resulted in a greater (P < 0.05) plasma IL-10 concentration. In conclusion, overall growth performance did not differ between HCP and LCP under CSC, but LCP diets reduced G:F under USC. Feeding LCP diets to weaned pigs improved gut morphology under USC and ameliorated systemic inflammation induced by USC, whereas CAA supplementation patterns did not affect growth performance and gut morphology.

A Mixture of Valine and Isoleucine Restores the Growth of Protein-Restricted Pigs Likely through Improved Gut Development, Hepatic IGF-1 Pathway, and Plasma Metabolomic Profile

Valine (Val) alone or in combination with isoleucine (Ile) improves the growth under severe protein restriction; however, the underlying mechanisms remain unknown. In this study, we assessed whether Val/Ile-induced growth in protein-restricted pigs is associated with changes in gut development, hepatic insulin-like growth factor 1 (IGF-1) production, and blood metabolomics. Forty piglets were assigned to five dietary groups: positive control (PC) with standard protein content; low protein (LP) with very low protein content; and LP supplemented with Val (LPV), Ile (LPI), and Val and Ile (LPVI). LPVI reversed the negative effects of VLP diets on growth and gut morphology. Both LPV and LPVI restored the reduced transcript of IGF-1 while decreasing the transcript of insulin-like growth factor binding protein 1 (IGFBP1) in the liver. LPV and LPVI recovered the reduced plasma Val, glycine, and leucine concentrations, which were positively correlated with improved gut morphology and the hepatic IGF-1 gene expression and negatively correlated with hepatic IGFBP1 mRNA abundance. In conclusion, supplementation with a combination of Val and Ile into the VLP diets restored the decreased growth performance of pigs fed with these diets likely through improved gut development, hepatic IGF-1 expression and bioavailability, and plasma metabolomics profile.

Nutritional stimulation by in-ovo feeding modulates cellular proliferation and differentiation in the small intestinal epithelium of chicks

Nutritional stimulation of the developing small intestine of chick embryos can be conducted by in-ovo feeding (IOF). We hypothesized that IOF of glutamine and leucine can enhance small intestinal development by promoting proliferation and differentiation of multipotent small intestinal epithelial cells. Broiler embryos (n = 128) were subject to IOF of glutamine (IOF-Gln), leucine (IOF-Leu), NaCl (IOF-NaCl) or no injection (control) at embryonic d 17 (E 17). Multipotent, progenitor and differentiated cells were located and quantified in the small intestinal epithelium between E 17 and d 7 after hatch (D 7) in all treatment groups by immunofluorescence of SRY-box transcription factor 9 (Sox9) and proliferating cell nuclear antigen (PCNA), in-situ hybridization of leucine-rich repeat containing G-protein coupled receptor 5 (Lgr5) and peptide transporter 1 (PepT1) and histochemical goblet cell staining. The effects of IOF treatments at E 19 (48 h post-IOF), in comparison to control embryos, were as follows: total cell counts increased by 40%, 33% and 19%, and multipotent cell counts increased by 52%, 50% and 38%, in IOF-Gln, IOF-Leu and IOF-NaCl embryos, respectively. Only IOF-Gln embryos exhibited a significance, 36% increase in progenitor cell counts. All IOF treatments shifted Lgr5+ stem cell localizations to villus bottoms. The differentiated, PepT1+ region of the villi was 1.9 and 1.3-fold longer in IOF-Gln and IOF-Leu embryos, respectively, while goblet cell densities decreased by 20% in IOF-Gln embryos. Post–hatch, crypt and villi epithelial cell counts were significantly higher IOF-Gln chicks, compared to control chicks (P < 0.05). We conclude IOF of glutamine stimulates small intestinal maturation and functionality during the peri-hatch period by promoting multipotent cell proliferation and differentiation, resulting in enhanced compartmentalization of multipotent and differentiated cell niches and expansions of the absorptive surface area.

Effect of traditional chinese medicine (TCM) and its fermentation using Lactobacillus plantarum on ceftriaxone sodium-induced dysbacteriotic diarrhea in mice

Background

Buzhongyiqi decoction (BD), Sijunzi decoction (SD), and Shenlingbaizhu decoction (SHD) have been extensively used clinically for the treatment of diseases caused by spleen-Qi deficiency and microbial fermentation has historically been utilized in traditional Chinese medicine (TCM). This study aimed to investigate the mitigative effect of TCM and fermented TCM (FTCM) with Lactobacillus plantarum (LP) on antibiotic-associated diarrhea, and to select an optimal formula and then identify its compounds.

Methods

Dysbacteriosis in mice was induced by ceftriaxone sodium (CS). The mice were then treated with LP, BD, SD, SHD, fermented BD, fermented SD (FSD), and fermented SHD. Diarrhea indexes, the abundances of gut bacteria, intestinal morphometrics, and mRNA expressions of genes related to intestinal barrier function were assessed. Then, ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) were employed to identify and relatively quantify the compounds in the selected decoctions.

Results

CS significantly increased the fecal output weight, the total number of fecal output, and fecal water content, indicating the occurrence of diarrhea. Bacterial culture tests showed that the above symptoms were accompanied by the disruption of specific intestinal flora. TCM, LP, and FTCM alleviated the diarrhea index and recovered the intestinal microbiota. FTCM showed more advantageous than TCM or LP alone. The mRNA expressions of aquaporins (AQPs) and tight junctions (TJs) decreased by CS were enhanced by TCM, LP, and FTCM. In addition, through UHPLC-Q-TOF/MS, (S)-(-)-2-hydroxyisocaproic acid, L-methionine, 4-guanidinobutyric acid (4GBA), and phenyllactate (PLA) in SD and FSD were identified and relatively quantified.

Conclusions

TCM, LP, and TCM fermented with LP alleviated CS-induced diarrhea symptoms, and improved the intestinal flora and barrier function. Four compounds including (S)-(-)-2-hydroxyisocaproic acid, L-methionine, 4GBA, and PLA in FSD, which were identified by UHPLC-Q-TOF/MS, might function in modulating intestinal flora and improving villi structure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-022-00575-x.

Functional role of branched chain amino acids in poultry: a review

This review provides insight into the effects of the branched-chain amino acids (BCAA: leucine, isoleucine, and valine) on the growth, production performance, immunity, and intestinal health of poultry. Besides providing nitrogen substrates and carbon framework for energy homeostasis and transamination, BCAA also function as signaling molecules in the regulation of glucose, lipid, and protein synthesis via protein kinase B and as a mechanistic target of the rapamycin (AKT-mTOR) signaling pathway that is important for muscle accretion. The level of leucine is generally high in cereals and an imbalance in the ratio among the 3 BCAA in a low protein diet would produce a negative effect on poultry growth performance. This occurs due to the structural similarity of the 3 BCAA, which leads to metabolic competition and interference with the enzymatic degradation pathway. Emerging evidence shows that the inclusion of BCAA is essential for the proper functioning of the innate and adaptive immune system and the maintenance of intestinal mucosal integrity. The recommended levels of BCAA for poultry are outlined by NRC (1994), but commercial broilers and laying hen breed standards also determine their own recommended levels. In this review, it has been noted that the requirement for BCAA is influenced by the diet type, breed, and age of the birds. Additionally, several studies focused on the effects of BCAA in low protein diets as a strategy to reduce nitrogen excretion. Notably, there is limited research on the inclusion ratio of BCAA in a supplemental form as compared to the ingredient-bound form which would affect the dynamics of utilization in different disease-challenged conditions, especially those affecting digesta passage ratio. In summary, this review encompasses the role of BCAA as functional AA and discusses their physiological effects on the productivity and health of poultry. The observations and interpretations of this review can guide future research to adjust the recommended levels of BCAA in feeding programs in the absence of subtherapeutic antibiotics in poultry.

A mix of functional amino acids and grape polyphenols promotes the growth of piglets, modulates the gut microbiota in vivo and regulates epithelial homeostasis in intestinal organoids

Weaning is a challenging period for gut health in piglets. Previous studies showed that dietary supplementations with either amino acids or polyphenols promote piglet growth and intestinal functions, when administered separately. Thus, we hypothesized that a combination of amino acids and polyphenols could facilitate the weaning transition. Piglets received during the first two weeks after weaning a diet supplemented or not with a mix of a low dose (0.1%) of functional amino acids (L-arginine, L-leucine, L-valine, L-isoleucine, L-cystine) and 100 ppm of a polyphenol-rich extract from grape seeds and skins. The mix of amino acids and polyphenols improved growth and feed efficiency. These beneficial effects were associated with a lower microbiota diversity and a bloom of Lactobacillaceae in the jejunum content while the abundance of Proteobacteria was reduced in the caecum content. The mix of amino acids and polyphenols also increased the production by the caecum microbiota of short-chain fatty acids (butyrate, propionate) and of metabolites derived from amino acids (branched-chain fatty acids, valerate, putrescine) and from polyphenols (3-phenylpropionate). Experiments in piglet jejunum organoids revealed that the mix of amino acids and polyphenols upregulated the gene expression of epithelial differentiation markers while it reduced the gene expression of proliferation and innate immunity markers. In conclusion, the supplementation of a mix of amino acids and polyphenols is a promising nutritional strategy to manage gut health in piglets through the modulation of the gut microbiota and of the epithelial barrier.

Use of low dosage amino acid blends to prevent stress-related piglet diarrhea

Weaning is a challenging period for piglets associated with reduced feed intake, impairment of gut integrity, and diarrhea. Previous studies demonstrate that supplementation with single functional amino acids (AA) promote piglets' performance due to the improvement of intestinal health. Thus, we hypothesized that a combination of functional AA provided beyond the postulated requirement for growth could facilitate the weaning transition. Ninety piglets, initially stressed after weaning by 100 min overland transport, received a control diet or the same diet supplemented with a low-dosed (0.3%) mixture of AA (AAB-1: L-arginine, L-leucine, L-valine, L-isoleucine, L-cystine; AAB-2: L-arginine, L-leucine, L-valine, L-isoleucine, L-cystine, and L-tryptophan) for 28 days. Fecal consistency was ranked daily, growth performance was assessed weekly. On days 1 and 14 of the trial, blood samples were collected from a subset of 10 piglets per group to assess concentrations of insulin-like growth factor 1. After 28 days of feeding, tissues were obtained from the same piglets to analyze gut morphology and relative mRNA expression of genes related to gut function. Even if the stress response as indicated by rectal temperature was not different between the groups, pigs supplemented with AAB-2 showed firmer feces after weaning and less days with diarrhea compared to control. Furthermore, the jejunal expression of the MUC-2 gene was reduced (P < 0.05) in group AAB-2. Both AA mixtures increased crypt depth in the duodenum. Collectively, the given results indicate that 0.3% extra AA supplementation might alleviate postweaning diarrhea but did not alter growth performance of weanling piglets.

Arginine Regulates TOR Signaling Pathway through SLC38A9 in Abalone Haliotis discus hannai

Arginine plays an important role in the regulation of the target of the rapamycin (TOR) signaling pathway, and Solute Carrier Family 38 Member 9 (SLC38A9) was identified to participate in the amino acid-dependent activation of TOR in humans. However, the regulations of arginine on the TOR signaling pathway in abalone are still unclear. In this study, slc38a9 of abalone was cloned, and the slc38a9 was knocked down and overexpressed to explore its function in the regulation of the TOR signaling pathway. The results showed that knockdown of slc38a9 decreased the expression of tor, ribosomal s6 protein kinase (s6k) and eukaryotic translation initiation factor 4e (eif4e) and inhibited the activation of the TOR signaling pathway by arginine. Overexpression of slc38a9 up-regulated the expression of TOR-related genes. In addition, hemocytes of abalone were treated with 0, 0.2, 0.5, 1, 2 and 4 mmol/L of arginine, and abalones were fed diets with 1.17%, 1.68% and 3.43% of arginine, respectively, for 120 days. Supplementation of arginine (0.5–4 mmol/L) increased the expressions of slc38a9, tor, s6k and eif4e in hemocytes, and abalone fed with 1.68% of dietary arginine showed higher mRNA levels of slc38a9, tor, s6k and eif4e and phosphorylation levels of TOR, S6 and 4E-BP. In conclusion, the TOR signaling pathway of abalone can be regulated by arginine, and SLC38A9 plays an essential role in this regulation.

Branched-chain amino acids partially recover the reduced growth of pigs fed with protein-restricted diets through both central and peripheral factors

The objective of this study was to assess the growth efficiency of pigs fed with protein-restricted diets supplemented with branched-chain amino acids (BCAA) and limiting amino acids (LAA) above the recommended levels. Following 2 weeks of adaptation, 48 young barrows were weight matched and randomly assigned to 6 treatments (8 pigs/treatment) for 4 weeks: positive control (PC) with standard protein, negative control (NC) with very low protein containing LAA (i.e., Lys, Met, Thr and Trp) at recommended levels, and NC containing LAA 25% (L25), LAA 50% (L50), LAA+BCAA (i.e., Leu, Ile and Val) 25% (LB25) and LAA+BCAA 50% (LB50) more than recommendations. Feed intake (FI) and body weight (BW) were measured daily and weekly, respectively. At week 6, blood samples were collected, all pigs euthanized and tissue samples collected. The data were analyzed by univariate GLM or mixed procedure (SPSS) and the means were separated using paired Student's t-test followed by Benjamini-Hochberg correction. Relative to PC, NC had decreased FI, BW, unsupplemented plasma essential amino acids, serum insulin-like growth factor-I (IGF-I) and hypothalamic neuropeptide Y (NPY) (P < 0.01). Compared to NC, L25 or L50, LB50 had increased BW and serum IGF-I and decreased plasma serotonin and both LB25 and LB50 had higher FI, plasma BCAA, hypothalamic 5-hydroxytryptamine-receptor 2A and NPY and jejunal 5-hydroxytryptamine-receptor 7 (P < 0.01). Overall, supplementation of protein-restricted diets with increased levels of dietary BCAA partially recovered the negative effects of these diets on growth through improved IGF-I concentration and FI, which was associated with changed expression of serotonin receptors, blood AA and hypothalamic NPY.

Amino Acids in Swine Nutrition and Production

Amino acids are the building blocks of proteins in animals, including swine. With the development of new analytical methods and biochemical research, there is a growing interest in fundamental and applied studies to reexamine the roles and usage of amino acids (AAs) in swine production. In animal nutrition, AAs have been traditionally classified as nutritionally essential (EAAs) or nutritionally nonessential (NEAAs). AAs that are not synthesized de novo must be provided in diets. However, NEAAs synthesized by cells of animals are more abundant than EAAs in the body, but are not synthesized de novo in sufficient amounts for the maximal productivity or optimal health (including resistance to infectious diseases) of swine. This underscores the conceptual limitations of NEAAs in swine protein nutrition. Notably, the National Research Council (NRC 2012) has recognized both arginine and glutamine as conditionally essential AAs for pigs to improve their growth, development, reproduction, and lactation. Results of recent work have also provided compelling evidence for the nutritional essentiality of glutamate, glycine, and proline for young pigs. The inclusion of so-called NEAAs in diets can help balance AAs in diets, reduce the dietary levels of EAAs, and protect the small intestine from oxidative stress, while enhancing the growth performance, feed efficiency, and health of pigs. Thus, both EAAs and NEAAs are needed in diets to meet the requirements of pigs. This notion represents a new paradigm shift in our understanding of swine protein nutrition and is transforming pork production worldwide.

Management and Feeding Strategies in Early Life to Increase Piglet Performance and Welfare around Weaning: A Review

The performance of piglets in nurseries may vary depending on body weight, age at weaning, management, and pathogenic load in the pig facilities. The early events in a pig's life are very important and may have long lasting consequences, since growth lag involves a significant cost to the system due to reduced market weights and increased barn occupancy. The present review evidences that there are several strategies that can be used to improve the performance and welfare of pigs at weaning. A complex set of early management and dietary strategies have been explored in sows and suckling piglets for achieving optimum and efficient growth of piglets after weaning. The management strategies studied to improve development and animal welfare include: (1) improving sow housing during gestation, (2) reducing pain during farrowing, (3) facilitating an early and sufficient colostrum intake, (4) promoting an early social interaction between litters, and (5) providing complementary feed during lactation. Dietary strategies for sows and suckling piglets aim to: (1) enhance fetal growth (arginine, folate, betaine, vitamin B12, carnitine, chromium, and zinc), (2) increase colostrum and milk production (DL-methionine, DL-2-hydroxy-4-methylthiobutanoic acid, arginine, L-carnitine, tryptophan, valine, vitamin E, and phytogenic actives), (3) modulate sows' oxidative and inflammation status (polyunsaturated fatty acids, vitamin E, selenium, phytogenic actives, and spray dried plasma), (4) allow early microbial colonization (probiotics), or (5) supply conditionally essential nutrients (nucleotides, glutamate, glutamine, threonine, and tryptophan).

Effects of dietary leucine levels on intestinal antioxidant status and immune response for juvenile golden pompano (Trachinotus ovatus) involved in Nrf2 and NF-κB signaling pathway

The aim of the study was to evaluate the effects of dietary leucine level on growth performance, intestinal antioxidant status and immune response involved in Nrf2 and NF-κB signaling pathway in juvenile golden pompano (Trachinotus ovatus). A total of 450 juvenile golden pompano (9.15 ± 0.04 g) were fed three isonitrogenous diets with graded leucine levels [1.25% (control), 2.77% and 5.84%] for 8 weeks. The results showed that, compared with the control group, the WG was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05), and the 5.84% dietary leucine group had a tendency to increase. Compared to control group, 5.84% dietary leucine group significantly decreased the moisture and ash contents of whole body (P < 0.05), meanwhile, 2.77% dietary leucine group significantly decreased moisture content of whole body, but significantly improved the whole body crude lipid content (P < 0.05). Compared with the control group, the ALP level was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). Inversely, the AST and ALT activities were significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). Compared with the control group, GPx, T-AOC, SOD activities in group of 2.77% dietary arginine level were significantly increased (P < 0.05). However, MDA level showed a reverse trend, which was significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). 2.77% dietary leucine levels significantly increased the relative expressions of Nrf2, HO-1, Cu/Zn-SOD, Mn-SOD and CAT (P < 0.05). In contrast, the relative expression of Keap1 showed a converse trend. Compared with the control group, the relative expressions of NF-κB, TNF-α and IL1-β were significantly lowered in fish fed with 2.77% of dietary leucine (P < 0.05). Additionally, 2.77% dietary leucine level significantly improved the relative expressions of TGF-β and IL-10 (P < 0.05). The 2.77% dietary leucine level significantly increased the muscular thickness compared with 5.84% dietary leucine level (P < 0.05). Furthermore, compared with the control group, the villus height and goblet cell counts were significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). These results indicated that the optimum dietary leucine plays an important role in promoting growth, enhancing antioxidant and immunity to maintain the intestinal health status of juvenile golden pompano.

Rumen Microbiome and Metabolome of Tibetan Sheep (Ovis aries) Reflect Animal Age and Nutritional Requirement

The rumen microbiota plays an important role in animal functional attributes. These microbes are indispensable for the normal physiological development of the rumen, and may also convert the plant polysaccharides from grass into available milk and meat, making it highly valuable to humans. Exploring the microbial composition and metabolites of rumen across developmental stages is important for understanding ruminant nutrition and metabolism. However, relatively few reports have investigated the microbiome and metabolites across developmental stages in ruminants. Using 16S rRNA gene sequnecing, metabolomics and high-performance liquid chromatography techniques, we compared the rumen microbiota, metabolites and short chain fatty acids (SCFAs) between lambs and sub-adult Tibetan sheep (Ovis aries) from Qinghai-Tibetan Plateau. Bacteroidetes and Spirochaetae were enriched in sub-adult sheep, while Firmicutes and Tenericutes were more abundant in young individuals. The sub-adult individuals had higher alpha diversity values than those in young sheep. Metabolomics analysis showed that the content of essential amino acids and related gene functional pathways in rumen were different between the lambs and sub-adult population. L-Leucine that participates in valine, leucine and isoleucine biosynthesis was more abundant in the lambs, while phenylethylamine that takes part in phenylalanine metabolism was more enriched in the sub-adults. Both rumen microbial community structures and metabolite profiles were impacted by age, but rumen SCFA concentration was relatively stable between different age stages. Some specific microbes (e.g., Clostridium and Ruminococcaceae) were positively associated with L-Leucine but negatively correlated with phenylethylamine, implying that rumen microbes may play different roles for metabolite production at different ages. Mantel test analysis showed that rumen microbiota was significantly correlated with metabolomics and SCFA profiles. Our results indicates the close relationship between microbial composition and metabolites, and also reveal different nutritional requirement for different ages in ruminants, thus having important significance for regulating animal nutrition and metabolism by microbiome intervention.

Role of Gut Microbiota in Neuroendocrine Regulation of Carbohydrate and Lipid Metabolism via the Microbiota-Gut-Brain-Liver Axis

Gut microbiota play an important role in maintaining intestinal health and are involved in the metabolism of carbohydrates, lipids, and amino acids. Recent studies have shown that the central nervous system (CNS) and enteric nervous system (ENS) can interact with gut microbiota to regulate nutrient metabolism. The vagal nerve system communicates between the CNS and ENS to control gastrointestinal tract functions and feeding behavior. Vagal afferent neurons also express receptors for gut peptides that are secreted from enteroendocrine cells (EECs), such as cholecystokinin (CCK), ghrelin, leptin, peptide tyrosine tyrosine (PYY), glucagon-like peptide-1 (GLP-1), and 5-hydroxytryptamine (5-HT; serotonin). Gut microbiota can regulate levels of these gut peptides to influence the vagal afferent pathway and thus regulate intestinal metabolism via the microbiota-gut-brain axis. In addition, bile acids, short-chain fatty acids (SCFAs), trimethylamine-N-oxide (TMAO), and Immunoglobulin A (IgA) can also exert metabolic control through the microbiota-gut-liver axis. This review is mainly focused on the role of gut microbiota in neuroendocrine regulation of nutrient metabolism via the microbiota-gut-brain-liver axis.

Dietary leucine supplementation improves intestinal health of mice through intestinal SIgA secretion

AIMS

Leucine supplementation promotes intestinal health, but the mechanism is largely unknown. This study aimed to elucidate the mechanisms underlying the beneficial effects of leucine on intestinal homeostasis.

METHODS AND RESULTS

Female ICR mice (6-week-old) were randomly assigned into three groups: (i) mice received a basal diet; (ii) mice received a dietary 0·5% crystalline l-leucine supplementation; and (iii) mice received a dietary 1·0% crystalline l-leucine supplementation. Our results showed that leucine supplementation stimulated the secretion of SIgA in mice ileum and expression of cytokines related to SIgA production. Moreover, leucine supplementation improved the expression of mTOR and p70S6K1 expression. Further study showed that leucine supplementation markedly decreased microbiota richness and induced a shift in the Firmicutes : Bacteroidetes ratio in favour of Firmicutes.

CONCLUSIONS

Therefore, our data suggested that leucine supplementation could enhance intestinal health through the regulation of mTOR pathway and promoting SIgA secretion in the mouse intestine, which might be associated with intestinal microbiota.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study found that dietary leucine supplementation of mice could improve intestinal health by enhancing intestinal SIgA secretion via a nonexclusive mechanism, which might include T cell-dependent pathway, T cell-independent pathway and gut microbiota.

Manipulation of Intestinal Antiviral Innate Immunity and Immune Evasion Strategies of Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) infection causes watery diarrhea, dehydration, and high mortality in neonatal pigs, due to its clinical pathogenesis of the intestinal mucosal barrier dysfunction. The host's innate immune system is the first line of defence upon virus invasion of the small intestinal epithelial cells. In turn, the virus has evolved to modulate the host's innate immunity during infection, resulting in pathogen virulence, survival, and the establishment of successful infection. In this review, we gather current knowledge concerning the interplay between PEDV and components of host innate immunity, focusing on the role of cytokines and interferons in intestinal antiviral innate immunity, and the mechanisms underlying the immune evasion strategies of PEDV invasion. Finally, we provide some perspectives on the potential prevention and treatment for PEDV infection.

l-Glutamine Represses the Unfolded Protein Response in the Small Intestine of Weanling Piglets

BACKGROUND

Dysfunction of the endoplasmic reticulum (ER) results in apoptosis, inflammation, and enhanced proteolysis in the small intestine of humans and animals. l-Glutamine (Gln) is required for intestinal mucosal homeostasis in piglets. However, a functional role of the ER in the enterocytes of weanling piglets and its contribution to intestinal mucosal integrity remain largely unknown.

OBJECTIVE

This study was conducted to test the hypothesis that preweaning administration of Gln alleviates the activation of unfolded protein response (UPR) in the small intestine of weanling piglets.

METHODS

Eighteen sow-reared piglets aged 7 d from 3 litters (6 piglets/litter) were assigned randomly into 1 of 3 treatment groups. Piglets were reared by sows until age 24 d, or were reared by sows and orally administered either l-alanine [1.84 g · kg body weight (BW)-1 · d-1] or Gln (1.52 g · kg BW-1 · d-1) twice daily between 7 and 21 d of age, and then weaned to a corn- and soybean meal-based diet. The small-intestinal samples were collected at 24 d of age for analyses of abundance of proteins related to ER stress and apoptosis, concentrations of inflammatory cytokines, and mRNA abundance for genes implicated in protein degradation.

RESULTS

Compared with age-matched suckling piglets, weaning stress increased apoptosis and decreased cell proliferation in the jejunum. The abundance of proteins related to ER stress [binding immunoglobulin protein, activating transcription factor 6α, phosphorylated (p)-inositol-requiring kinase 1α, and p-eukaryotic initiation factor 2α] was elevated by 200% to 320%, and that of apoptotic proteins (CCAAT/enhancer-binding protein homologous protein, p-Jun-N-terminal kinase, caspase-12, cleaved caspase-3, and Bcl-2-associated X) was augmented by 100% to 350% in the jejunum of weanling piglets. The protein abundance for IL-1β, TNF-α, and IL-8 was increased by 100% to 230% in the jejunum of weanling piglets. These alterations in gene and protein expression were markedly abrogated by Gln supplementation. The mRNA concentration of F-Box protein 32 in the jejunum of weanling piglets was increased by 70%, compared with the control group, and was not affected by Gln supplementation.

CONCLUSION

Our results indicate that preweaning administration of Gln to nursing piglets alleviates the weaning-activated UPR.

Dietary Branched-Chain Amino Acids Regulate Food Intake Partly through Intestinal and Hypothalamic Amino Acid Receptors in Piglets

Strategies to increase feed intake are of great importance for producing more meat in swine production. Intestinal and hypothalamic amino acid receptors are found to largely participate in feed intake regulation. The purpose of the current research is to study the function of branched-chain amino acid (BCAA) supplementation in the regulation of feed intake through sensors that can detect amino acids in piglets. Twenty-four piglets were assigned one of four treatments and fed one of the experimental diets for either a short period (Expt. 1) or a long period (Expt. 2): a normal protein diet (NP, 20.04% CP), a reduced-protein diet (RP, 17.05% CP), or a reduced-protein test diet supplemented with one of two doses of BCAAs (BCAA1, supplemented with 0.13% l-isoleucine, 0.09% l-leucine, and 0.23% l-valine; BCAA2, supplemented with the 150% standardized ileal digestibility BCAA requirement, as recommended by the National Research Council (2012)). In Expt. 1, no differences were observed in the feed intake among piglets fed different diets ( P > 0.05). In Expt. 2, compared with the RP group, the feed intake of piglets was significantly increased after sufficient BCAAs were supplemented in the BCAA1 group, which was associated with decreased cholecystokinin secretion ( P < 0.05), down-regulated expression of type-1 taste receptors 1/3 (T1R1/T1R3) in the intestine, as well as increased expression of pro-opiomelanocortin, activated general control nonderepressible 2 (GCN2), and eukaryotic initiation factor 2α (eIF2α) in the hypothalamus ( P < 0.05). However, the feed intake was decreased for unknown reasons when the piglets were fed a BCAA over-supplemented diet. Our study confirmed that a BCAA-deficient diet inhibited feed intake through two potential ways: regulating the amino acid T1R1/T1R3 receptor in the intestine or activating GCN2/eIF2α pathways in the hypothalamus.

Immunocrit, serum amino acid concentrations and growth performance in light and heavy piglets depending on sow's farrowing system

Background

The conventional farrowing crate is criticised due to the limited mobility of sows during farrowing and lactation. The present study aims to investigate the effects of three different farrowing systems on the performance of suckling neonates on the basis of immunocrit (IC; a quantification of immunoglobulins), serum amino acid (AA) concentrations and growth performance.

Methods

From a total of 149 sows placed in three housing systems (farrowing crate – FC, loose housing – LH, group housing – GH), 18 sows and their respective litters, formed the basis for a two-factorial study design (farrowing system and body weight (BW) of neonates). Therefore, also blood samples of two light (1.0–1.4 kg) and two heavy (≥ 1.4 kg) piglets were taken within 48 h post natum (p.n.) and on the day of weaning (day 26) to determine the immunocrit (IC; a quantification of immunoglobulins) and levels of serum AAs.

Results

The IC (FC: 0.148^a, LH: 0.153^a, GH: 0.117^b) as well as serum levels of arginine, leucine, lysine, proline and threonine within 48 h p.n. were significantly lower in GH. Additionally, in general, these piglets showed (except for the first week of life) the lowest average daily weight gain. On the day of weaning, piglets in GH had the lowest levels of arginine (in mg/dL; FC: 3.68^a, LH: 3.40^ab, GH: 2.94^b) and threonine (in mg/dL; FC: 3.59^a, LH: 3.02^ab, GH: 2.49^b). The concentrations of leucine, lysine, proline and valine at this time were significantly lower in LH.

Conclusion

The observed significant lower IC indicates a lower Ig intake of piglets in the tested GH. No significant differences regarding the IC and AA levels within 48 h p.n. of the piglets in FC and LH could be seen. In principle, differences at weaning in AA levels were rather small, although the body weight of GH piglets at weaning was lower. Therefore, further research needs to clarify whether there are medium-term effects on health and performance.

Electronic supplementary material

The online version of this article (10.1186/s40813-019-0121-1) contains supplementary material, which is available to authorized users.

Amino Acids Influencing Intestinal Development and Health of the Piglets

Simple Summary

The health of piglets is an important issue in pig production. Nutritional support for intestinal development is a significant component of piglet care, and amino acids are essential for intestinal growth and development. For suckling piglets, the sows’ milk and the maternal environment shape the structure and support the function of the intestinal tract. The composition of milk affects intestinal morphology and the digestive, absorption and barrier function. After weaning, the optimal nutritional strategies of their diet are necessary to guarantee the piglets’ intestinal development and growth performance. Amino acids are the most important ingredient in piglet diets. The aim of this review is to collect and analyze the relationship between amino acid nutrition and intestinal development of piglets, and elucidate the impacts on piglet health.

Abstract

The amino acids and other components of diet provide nourishment for piglet intestinal development and maturation. However, early-weaned piglets struggle with tremendous stress, impairing normal intestinal health and leading to intestinal dysfunction and even death. The high prevalence worldwide of post-weaning diarrhoea syndrome (PWDS) in piglets has led to much interest in understanding the important role of nutrients in the establishment and maintenance of a functional intestinal tract. In particular, the impacts of amino acids on these functions must be considered. Amino acid levels greatly influence intestinal development in weaning piglets. The lack of amino acids can cause marked structural and functional changes in the intestine. Therefore, a comprehensive understanding of the functions of amino acids is necessary to optimize amino acid requirements of the developing intestinal tract to maximize piglet health and growth performance. This review summarizes the role of specific amino acids (arginine, glutamate, threonine, sulphur-containing amino acids (SCAAs), and branched-chain amino acids (BCAAs)) that have been proven to be beneficial for the intestinal health of weaned piglets.

Intervening Effects of Total Alkaloids of Corydalis saxicola Bunting on Rats With Antibiotic-Induced Gut Microbiota Dysbiosis Based on 16S rRNA Gene Sequencing and Untargeted Metabolomics Analyses

Gut microbiota dysbiosis induced by antibiotics is strongly connected with health concerns. Studying the mechanisms underlying antibiotic-induced gut microbiota dysbiosis could help to identify effective drugs and prevent many serious diseases. In this study, in rats with antibiotic-induced gut microbiota dysbiosis treated with total alkaloids of Corydalis saxicola Bunting (TACS), urinary and fecal biochemical changes and cecum microbial diversity were investigated using 16S rRNA gene sequencing analysis and untargeted metabolomics. The microbial diversity results showed that 10 genera were disturbed by the antibiotic treatment, and two of them were obviously restored by TACS. The untargeted metabolomics analysis identified 34 potential biomarkers in urine and feces that may be the metabolites that are most related to the mechanisms underlying antibiotic-induced gut microbiota dysbiosis and the therapeutic effects of TACS treatment. The biomarkers were involved in six metabolic pathways, comprising pathways related to branched-chain amino acid (BCAA), bile acid, arginine and proline, purine, aromatic amino acid, and amino sugar and nucleotide sugar metabolism. Notably, there was a strong correlation between these metabolic pathways and two gut microbiota genera (g__Blautia and g__Intestinibacter). The correlation analysis suggested that TACS might synergistically affect four of these metabolic pathways (BCAA, bile acid, arginine and proline, and purine metabolism), thereby modulating gut microbiota dysbiosis. Furthermore, we performed a molecular docking analysis involving simulating high-precision docking and using molecular pathway maps to illuminate the way that ligands (the five main alkaloid components of TACS) act on a complex molecular network, using CYP27A1 (a key enzyme in the bile acid synthesis pathway) as the target protein. This study provides a comprehensive overview of the intervening effects of TACS on the host metabolic phenotype and gut microbiome in rats with gut microbiota dysbiosis, and it presents new insights for the discovery of effective drugs and the best therapeutic approaches.

Effects of dietary leucine and phenylalanine on gastrointestinal development and small intestinal enzyme activities in milk-fed holstein dairy calves

This study was investigated the effects of dietary supplementation of leucine and phenylalanine on the development of the gastrointestinal tract and the intestinal digestive enzyme activity in male Holstein dairy calves. Twenty calves with a body weight of 38 ± 3 kg at 1 day of age were randomly divided into four groups: a control group, a leucine group (1.435 g·l⁻¹), a phenylalanine group (0.725 g·l⁻¹), and a mixed amino acid group (1.435 g·l⁻¹ leucine plus 0.725 g·l⁻¹ phenylalanine). The supplementation of leucine decreased the short-circuit current (Isc) of the rumen and duodenum (P<0.01); phenylalanine did not show any influence on the Isc of rumen and duodenum (P>0.05), and also counteracted the Isc reduction caused by leucine. Leucine increased the trypsin activity at the 20% relative site of the small intestine (P<0.05). There was no difference in the activity of α-amylase and of lactase in the small intestinal chyme among four treatments (P>0.05). The trypsin activity in the anterior segment of the small intestine was higher than other segments, whereas the α-amylase activity in the posterior segment of the small intestine was higher than other segments. Leucine can reduce Isc of the rumen and duodenum, improve the development of the gastrointestinal tract, and enhance trypsin activity; phenylalanine could inhibit the effect of leucine in promoting intestinal development.

Physiological Effects of Dietary Amino Acids on Gut Health and Functions of Swine

Gut health has significant implications for swine overall health status and nutrient utilization, due to its various functions including digestion and absorption of nutrients, secretion of mucins and immunoglobulins, and selective barrier protection against harmful antigens and pathogens. Both the basic anatomical structure of the gut (such as epithelial cells) and its luminal microbiota play important roles for maintaining gut health and functions. The interactions between epithelial cells and luminal microbiota have significant impact on host nutrition and health through the metabolism of dietary components. Amino acids, which are major nutrients for pigs, are not only obligatory for maintaining the intestinal mucosal mass and integrity, but also for supporting the growth of microorganisms in the gut. Dietary amino acids are the major fuel of the small intestinal mucosa. Particularly, glutamate, glutamine, and aspartate are the major oxidative fuel of the intestine. Emerging evidence shows that arginine activates the mTOR signaling pathway in the small intestine. Utilization of glycine by the small intestinal mucosa to synthesize glutathione is a very important physiological pathway, and the role of glycine as a powerful cytoprotectant has also been recognized. The major end products of methionine and cysteine metabolism are glutathione, homocysteine and taurine, which play important roles in the intestinal immune and anti-oxidative responses. Threonine is highly utilized by the gut and is particularly important for mucin synthesis and maintenance of gut barrier integrity. Moreover, either a deficiency or an excess of dietary threonine can reduce the synthesis of intestinal mucosal proteins and mucins in young pigs. Various new functions of amino acids on gut health and functions have been discovered in recent years. Thus, this review is to provide some up-to-date knowledge for industry application of dietary amino acids in order to enhance swine gut health and functions, and also it is to provide a comprehensive reference for further scientific research in this regard.

Exploration of the Relationship between Intestinal Colostrum or Milk, and Serum Metabolites in Neonatal Calves by Metabolomics Analysis

In contrast to colostral immunoglobulins, changes in metabolite composition of ingested colostrum in the gut have received little attention. Here, we characterized the metabolite profiles of colostrum and milk, ingested colostrum and milk, and serum of neonatal calves by liquid chromatography tandem-mass spectrometry and gas chromatography-mass spectrometry metabolomics approaches. Colostrum and milk underwent similar changes in metabolite profiles in the gut after being ingested. These changes were characterized by increases in methionine, glutamate, thymine, and phosphorylcholine. After ingestion, colostrum concentrations of several metabolites, such as γ-aminobutyric acid, glutamate, cinnamic acid, and thymine increased, whereas concentrations of d-ribose, and arginine decreased. These increases and decreases occurred in a time-dependent manner and were associated with alanine, aspartate, glutamate, and pyrimidine metabolism, and valine, leucine, and isoleucine biosynthesis, respectively. Meanwhile, similar changes in serum metabolites were also observed in neonatal calves fed colostrum, which implies that colostrum metabolites are transported across the small intestine and into the bloodstream. In addition, several metabolites of ingested milk were detected in the gut, and were also transferred to the bloodstream. These metabolites were related to phenylalanine, tyrosine, tryptophan, valine, leucine, and isoleucine biosynthesis, the citrate cycle, and histidine metabolism. These findings reveal that the serum metabolome of neonatal calves' changes as a result of ingesting colostrum, which can provide health-related benefits in early life.

Leucine Promotes the Growth of Fetal Pigs by Increasing Protein Synthesis through the mTOR Signaling Pathway in Longissimus Dorsi Muscle at Late Gestation

Leucine (Leu) plays an important role in protein synthesis and metabolism. The present study tested whether Leu supplementation in the diet for sows during late pregnancy could improve piglet birth weight, and it also investigated the possible underlying mechanism. Two hundred sows at day 70 of pregnancy were selected and assigned to four groups fed with following four diets until farrowing, respectively: corn and soybean meal-based diet group (CON), CON + 0.40% Leu, CON + 0.80% Leu, and CON + 1.20% Leu. We found that supplementing with 0.80% Leu significantly increased mean piglet birth weight ( P < 0.05). Supplementation with 0.40, 0.80, and 1.20% Leu increased the plasma concentration of Leu, while decreasing the plasma concentrations of valine (Val) and isoleucine (Ile) in both farrowing sows and newborn piglets ( P < 0.05). The protein expressions of amino acid transporters (including LAT1, SNAT1, SNAT2, 4F2hc, and rBAT) in duodenum, jejunum, ileum, longissimus dorsi muscle of newborn piglets, and placenta of sows showed a difference among the CON group and Leu supplemented groups. Expressions of p-mTOR, p-4E-BP1, and p-S6K1 in longissimus dorsi muscle were also enhanced in each of the supplemental Leu groups compared to CON ( P < 0.05). Collectively, these results indicated that 0.40-0.80% Leu supplementation during late gestation enhanced birth weight of fetal pigs by increasing protein synthesis through modulation of the plasma amino acids profile, amino acid transporters expression, and mTOR signaling pathway.

CDX2 increases SLC7A7 expression and proliferation of pig intestinal epithelial cells

Nutrient absorption mediated by nutrient transporters expressed in the intestinal epithelium supplies substrates to support intestinal processes, including epithelial cell proliferation. We evaluated the role of Caudal type homeobox 2 (CDX2), an intestine-specific transcription factor, in the proliferation of pig intestinal epithelial cells (IPEC-1) and searched for novel intestinal nutrient transporter genes activated by CDX2. Our cloned pig CDX2 cDNA contains a “homeobox” DNA binding motif, suggesting it is a transcriptional activator. CDX2 overexpression in IPEC-1 cells increased cell proliferation, the percentage of cells in S/G2 phase, and the abundance of transcripts of the cell cycle-related genes Cyclin A2; Cyclin B; Cyclin D2; proliferating cell nuclear antigen; and cell cycle cyclin-dependent kinases 1, 2 and 4, as well as the predicted CDX2 target genes SLC1A1, SLC5A1 and SLC7A7. In addition, luciferase reporter and chromatin immunoprecipitation assays revealed that CDX2 binds directly to the SLC7A7 promoter. This is the first report of CDX2 function in pig intestinal epithelial cells and identifies SLC7A7 as a novel CDX2 target gene. Our findings show that nutrient transporters are activated during CDX2-induced proliferation of normal intestinal epithelial cells.

Regulation of intestinal health by branched-chain amino acids

Besides its primary role in the digestion and absorption of nutrients, the intestine also interacts with a complex external milieu, and is the first defense line against noxious pathogens and antigens. Dysfunction of the intestinal barrier is associated with enhanced intestinal permeability and development of various gastrointestinal diseases. The branched-chain amino acids (BCAAs) are important nutrients, which are the essential substrates for protein biosynthesis. Recently, emerging evidence showed that BCAAs are involved in maintaining intestinal barrier function. It has been reported that dietary supplementation with BCAAs promotes intestinal development, enhances enterocyte proliferation, increases intestinal absorption of amino acids (AA) and glucose, and improves the immune defenses of piglets. The underlying mechanism of these effects is mediated by regulating expression of genes and proteins associate with various signaling pathways. In addition, BCAAs promote the production of beneficial bacteria in the intestine of mice. Compelling evidence supports the notion that BCAAs play important roles in both nutrition and intestinal health. Therefore, as functional amino acids with various physiological effects, BCAAs hold key roles in promoting intestinal development and health in animals and humans.