Effect of High Dietary Tryptophan on Intestinal Morphology and Tight Junction Protein of Weaned Pig

ACE2 mediates tryptophan alleviation on diarrhea by repairing intestine barrier involved mTOR pathway

The membrane-delimited receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), angiotensin-converting enzyme 2 (ACE2), which is expressed in the intestine, collaborates with broad neutral amino acid transporter 1 (B0AT1). Tryptophan (Trp) is transported into intestinal epithelial cells by ACE2 and B0AT1. However, whether ACE2 and its binding protein B0AT1 are involved in Trp-mediated alleviation of intestinal injury is largely unknown. Here, we used weaned piglets and IPEC-J2 cells as models and found that ACE2/B0AT1 alleviated lipopolysaccharide (LPS)-induced diarrhea and promoted intestinal barrier recovery via transport of Trp. The levels of the aryl hydrocarbon receptor (AhR) and mechanistic target of rapamycin (mTOR) pathways were altered by ACE2. Dietary Trp supplementation in LPS-treated weaned piglets revealed that Trp alleviated diarrhea by promoting ACE2/B0AT1 expression, and examination of intestinal morphology revealed that the damage to the intestinal barrier was repaired. Our study demonstrated that ACE2 accompanied by B0AT1 mediated the alleviation of diarrhea by Trp through intestinal barrier repair via the mTOR pathway.

CXCR2, as a key regulatory gene of HDP-PG-1, maintains intestinal mucosal homeostasis

The intestine defends against pathogenic microbial invasion via the secretion of host defense peptides (HDPs). Nutritional immunomodulation can stimulate the expression of endogenous HDPs and enhance the body's immune defense, representing a novel non-antibiotic strategy for disease prevention. The project aims to explore the regulatory mechanism of protegrin-1 (PG-1) expression using sodium phenylbutyrate (PBA) by omics sequencing technology and further investigate the role of key regulatory genes on intestinal health. The results showed that PBA promoted PG-1 expression in intestinal epithelial cells based on cell density through epidermal growth factor receptor (EGFR) and G protein-coupled receptor (GPR43). Transcriptome sequencing and microRNA sequencing revealed that C-X-C motif chemokine receptor 2 (CXCR2) exhibited interactions with PG-1. Pre-treatment cells with a CXCR2 inhibitor (SB225002) effectively suppressed the induction of PG-1 by PBA. Furthermore, SB225002 significantly suppressed the gene expression of HDPs in the jejunum of mice without influencing on the morphology, number of goblet cells, and proliferation of the intestine. CXCR2 inhibition significantly reduced the expression of HDPs during E. coli infection, and resulted in the edema of jejunal epithelial cells. The 16S rDNA analysis of cecal contents showed that the E. coli and SB225002 treatments changed gut microbiota diversity and composition at different taxonomic levels. Correlation analysis suggested a potential regulatory relationship between gut microbiota and HDPs. To that end, a gene involved in the HDP expression, CXCR2, has been identified in the study, which contributes to improving intestinal immune function. PBA may be used as a functional additive to regulate intestinal mucosal function, thereby enhancing the health of the intestinal and host.

Tryptophan metabolism and piglet diarrhea: Where we stand and the challenges ahead

The intestinal architecture of piglets is vulnerable to disruption during weaning transition and leads to diarrhea, frequently accompanied by inflammation and metabolic disturbances (including amino acid metabolism). Tryptophan (Trp) plays an essential role in orchestrating intestinal immune tolerance through its metabolism via the kynurenine, 5-hydroxytryptamine, or indole pathways, which could be dictated by the gut microbiota either directly or indirectly. Emerging evidence suggests a strong association between piglet diarrhea and Trp metabolism. Here we aim to summarize the intricate balance of microbiota-host crosstalk by analyzing alterations in both the host and microbial pathways of Trp and discuss how Trp metabolism may affect piglet diarrhea. Overall, this review could provide valuable insights to explore effective strategies for managing piglet diarrhea and the related challenges.

Culture media and format alter cellular composition and barrier integrity of porcine colonoid-derived monolayers

Intestinal organoid technology has revolutionized our approach to in vitro cell culture due in part to their three-dimensional structures being more like the native tissue from which they were derived with respect to cellular composition and architecture. For this reason, organoids are becoming the new gold standard for undertaking intestinal epithelial cell research. Unfortunately, their otherwise advantageous three-dimensional geometry prevents easy access to the apical epithelium, which is a major limitation when studying interactions between dietary or microbial components and host tissues. To overcome this problem, we developed porcine colonoid-derived monolayers cultured on both permeable Transwell inserts and tissue culture treated polystyrene plates. We found that seeding density and culture format altered the expression of genes encoding markers of specific cell types (stem cells, colonocytes, goblets, and enteroendocrine cells), and barrier maturation (tight junctions). Additionally, we found that changes to the formulation of the culture medium altered the cellular composition of colonoids and of monolayers derived from them, resulting in cultures with an increasingly differentiated phenotype that was similar to that of their tissue of origin.

Dietary tryptophan improves growth and intestinal health by promoting the secretion of intestinal β-defensins against enterotoxigenic E. coli F4 in weaned piglets

Adequate dietary L-tryptophan (Trp) governs intestinal homeostasis in piglets. However, the defensive role of Trp in the diet against enterotoxigenic E. coli F4 (K88) in pigs is still poorly understood. Here, sixty (6.15 ± 1.52 kg, 24-day-old, Duroc × Landrace × Yorkshire) weaned piglets were used for an E. coli F4 attack test in a 2 × 2 factorial design. The growth (ADG, ADFI, GH), immune factors (IL-10, IgA, IgG, IgM), Trp metabolite 5-HT, intestinal morphology (jejunal and colonic VH), mRNA expression of β-defensins (jejunal BD-127, BD-119, ileal BD-1, BD-127), and abundance of beneficial microorganisms in the colon (Prevotella 9, Lactobacillus, Phascolarctobacterium, Faecalibacterium) were higher in the piglets in the HT (High Trp) and HTK (High Trp, K88) groups than in the LT (Low Trp) and LTK (Low Trp, K88) groups (P < 0.05), while FCR, diarrhea rate, diarrhea index, serum Trp, Kyn, IDO, D-LA, ET, and abundance of harmful microorganisms in the colon (Spirochaetes, Fusobacteria, Prevotella, Christensenellaceae R7) were lower in the HT and HTK groups than in the LT and LTK groups (P < 0.05). High Trp reduced the expression of virulence genes (K88 and LT) after E. coli F4 attack (P < 0.05). The IL-6, TNF-α was lower in the HTK group than in the LT, LTK group (P < 0.05). In short, a diet containing 0.35% Trp protected piglets from enterotoxigenic E. coli F4 (K88) via Trp metabolism promoting BD expression in the intestinal mucosa, which improved growth and intestinal health.

Low crude protein formulation with supplemental amino acids for its impacts on intestinal health and growth performance of growing-finishing pigs

BACKGROUND

Low crude protein (CP) formulations with supplemental amino acids (AA) are used to enhance intestinal health, reduce costs, minimize environmental impact, and maintain growth performance of pigs. However, extensive reduction of dietary CP can compromise growth performance due to limited synthesis of non-essential AA and limited availability of bioactive compounds from protein supplements even when AA requirements are met. Moreover, implementing a low CP formulation can increase the net energy (NE) content in feeds causing excessive fat deposition. Additional supplementation of functional AA, coupled with low CP formulation could further enhance intestinal health and glucose metabolism, improving nitrogen utilization, and growth performance. Three experiments were conducted to evaluate the effects of low CP formulations with supplemental AA on the intestinal health and growth performance of growing-finishing pigs.

METHODS

In Exp. 1, 90 pigs (19.7 ± 1.1 kg, 45 barrows and 45 gilts) were assigned to 3 treatments: CON (18.0% CP, supplementing Lys, Met, and Thr), LCP (16.0% CP, supplementing Lys, Met, Thr, Trp, and Val), and LCPT (16.1% CP, LCP + 0.05% SID Trp). In Exp. 2, 72 pigs (34.2 ± 4.2 kg BW) were assigned to 3 treatments: CON (17.7% CP, meeting the requirements of Lys, Met, Thr, and Trp); LCP (15.0% CP, meeting Lys, Thr, Trp, Met, Val, Ile, and Phe); and VLCP (12.8% CP, meeting Lys, Thr, Trp, Met, Val, Ile, Phe, His, and Leu). In Exp. 3, 72 pigs (54.1 ± 5.9 kg BW) were assigned to 3 treatments and fed experimental diets for 3 phases (grower 2, finishing 1, and finishing 2). Treatments were CON (18.0%, 13.8%, 12.7% CP for 3 phases; meeting Lys, Met, Thr, and Trp); LCP (13.5%, 11.4%, 10.4% CP for 3 phases; meeting Lys, Thr, Trp, Met, Val, Ile, and Phe); and LCPG (14.1%, 12.8%, 11.1% CP for 3 phases; LCP + Glu to match SID Glu with CON). All diets had 2.6 Mcal/kg NE.

RESULTS

In Exp. 1, overall, the growth performance did not differ among treatments. The LCPT increased (P < 0.05) Claudin-1 expression in the duodenum and jejunum. The LCP and LCPT increased (P < 0.05) CAT-1, 4F2hc, and B0AT expressions in the jejunum. In Exp. 2, overall, the VLCP reduced (P < 0.05) G:F and BUN. The LCP and VLCP increased (P < 0.05) the backfat thickness (BFT). In Exp. 3, overall, growth performance and BFT did not differ among treatments. The LCPG reduced (P < 0.05) BUN, whereas increased the insulin in plasma. The LCP and LCPG reduced (P < 0.05) the abundance of Streptococcaceae, whereas the LCP reduced (P < 0.05) Erysipelotrichaceae, and the alpha diversity.

CONCLUSIONS

When implementing low CP formulation, CP can be reduced by supplementation of Lys, Thr, Met, Trp, Val, and Ile without affecting the growth performance of growing-finishing pigs when NE is adjusted to avoid increased fat deposition. Supplementation of Trp above the requirement or supplementation of Glu in low CP formulation seems to benefit intestinal health as well as improved nitrogen utilization and glucose metabolism.

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.

Effects of Dietary Glutamine Supplementation on the Modulation of Microbiota and Th17/Treg Immune Response Signaling Pathway in Piglets after Lipopolysaccharide Challenge

BACKGROUND

Glutamine (Gln) has an important effect on the growth performance and immune function of piglets. However, the effect of Gln on intestinal immunity in piglets through modulating the signaling pathways of the helper T cells 17 (Th17)/regulatory T cells (Treg) immune response has not been reported.

OBJECTIVE

This study aimed to determine the effect of Gln on piglet growth performance and immune stress response and its mechanism in piglets.

METHODS

Twenty-four weaned piglets were randomly assigned to 4 treatments with 6 replicates each, using a 2 × 2 factorial arrangement: diet (basal diet or 1% Gln diet) and immunological challenge [saline or lipopolysaccharide (LPS)]. After 21 d, half of the piglets on the basal diet and 1% Gln diet received the intraperitoneal injection of LPS and the other half received the same volume of normal saline.

RESULTS

The results showed that Gln increased average daily feed intake and average daily weight gain in comparison with the control group (P < 0.05). Dietary Gln increased the villus height, villus height-to-crypt depth ratio, and the abundance of Bacteroidetes, Lactobacillus sp., and Ruminococcus sp. while reducing the abundance of Firmicutes, Clostridium sensu stricto 1 sp., and Terrisporobacter sp. (P < 0.05). Furthermore, Gln increased the concentration of short-chain fatty acids in the colon and the expression of genes of interleukin (IL)-10, transforming growth factor-beta-1, forkhead box P3 while downregulating the expression of genes of IL-6, IL-8, IL-1β, tumor necrosis factor-α, IL-17A, IL-21, signal transducer and activator of transcription 3, and rar-related orphan receptor c in ileum (P < 0.05). Correlation analysis demonstrated a strong association between colonic microbiota, short-chain fatty acids, and ileal inflammatory cytokines.

CONCLUSIONS

These results suggest that dietary Gln could improve growth performance and attenuate LPS-challenged intestinal inflammation by modulating microbiota and the Th17/Treg immune response signaling pathway in piglets.

Overview of the compromised mucosal integrity in celiac disease

Intestinal epithelium is a dynamic cellular layer that lines the small-bowel and makes a relatively impenetrable barrier to macromolecules. Intestinal epithelial cell polarity is crucial in coordinating signalling pathways within cells and mainly regulated by three conserved polarity protein complexes, the Crumbs (Crb) complex, partitioning defective (PAR) complex, and Scribble (Scrib) complex. Polarity proteins regulate the proper establishment of the intercellular junctional complexes including tight junctions (TJs), adherence junctions (AJs), and desmosomes which hold epithelial cells together and play a major role in maintaining intestinal barrier integrity. Impaired intestinal epithelial cell polarity and barrier integrity result in irreversible immune responses, the host- microbial imbalance and intestinal inflammatory disorders. Disassembling the epithelial tight junction and augmented paracellular permeability is a conspicuous hallmark of celiac disease (CD) pathogenesis. There are several dietary components that can improve intestinal integrity and function. The aim of this review article is to summarize current information about the association of polarity proteins and AJC damages with pathogenesis of CD.

Effects of Rumen-Protected L-Tryptophan Supplementation on Productivity, Physiological Indicators, Blood Profiles, and Heat Shock Protein Gene Expression in Lactating Holstein Cows under Heat Stress Conditions

In this study, we examined the effects of rumen-protected L-tryptophan supplementation on the productivity and physiological metabolic indicators in lactating Holstein cows under heat stress conditions. The study involved eight early lactating Holstein cows (days in milk = 40 ± 9 days; milk yield 30 ± 1.5 kg/day; parity 1.09 ± 0.05, p < 0.05), four cows per experiment, with environmentally controlled chambers. In each experiment, two distinct heat stress conditions were created: a low-temperature and low-humidity (LTLH) condition at 25 °C with 35-50% humidity and a high-temperature and high-humidity (HTHH) condition at 31 °C with 80-95% humidity. During the adaptation phase, the cows were subjected to LTLH and HTHH conditions for 3 days. This was followed by a 4-day heat stress phase and then by a 7-day phase of heat stress, which were complemented by supplementation with rumen-protected L-tryptophan (ACT). The findings revealed that supplementation with ACT increased dry matter intake as well as milk yield and protein and decreased water intake, heart rate, and rectal temperature in the HTHH group (p < 0.05). For plateletcrit (PCT, p = 0.0600), the eosinophil percentage (EOS, p = 0.0880) showed a tendency to be lower, while the monocyte (MONO) and large unstained cells (LUC) amounts were increased in both groups (p < 0.05). Albumin and glucose levels were lower in the HTHH group (p < 0.05). The gene expressions of heat shock proteins 70 and 90 in the peripheral blood mononuclear cells were higher in the ACT group (HTHH, p < 0.05). These results suggest that ACT supplementation improved productivity, physiological indicators, blood characteristics, and gene expression in the peripheral blood mononuclear cells of early lactating Holstein cows under heat-stress conditions. In particular, ACT supplementation objectively relieved stress in these animals, suggesting that L-tryptophan has potential as a viable solution for combating heat-stress-induced effects on the cattle in dairy farming.

Intestinal tryptophan metabolism in disease prevention and swine production

Tryptophan (Trp) is an essential amino acid that cannot be synthesized by animals. It has been characterized into two different isomers, levorotation-Trp (L-Trp) and dextrorotation-Trp (D-Trp), based on their distinct molecule orientation. Intestinal epithelial cells and gut microbiota are involved in metabolizing L-Trp in the gut via the activation of the kynurenine, serotonin, and indole pathways. However, knowledge regarding D-Trp metabolism in the gut remains unclear. In this review, we briefly update the current understanding of intestinal L/D-Trp metabolism and the function of their metabolites in modulating the gut physiology and diseases. Finally, we summarize the effects of Trp nutrition on swine production at different stages, including growth performance in weaned piglets and growing pigs, as well as the reproduction performance in sows.

Tryptophan alleviates intestinal damage through regulating necroptosis and TLR4/NOD signaling pathways in pigs after lipopolysaccharide challenge

This study aimed to test the hypothesis that necroptosis, toll-like receptor 4 (TLR4)/nucleotide-binding oligomerization domain (NOD) signaling pathway in the jejunum of lipopolysaccharide (LPS)-challenged piglets are involved in the alleviation of intestinal injury and inflammation by tryptophan supplementation. Tryptophan supplementation has improved intestinal morphology. Also, tryptophan has been found to increase the mRNA and protein expression of tight junction proteins and decrease the expression of pro-inflammatory cytokines. Dietary tryptophan decreased the mRNA expression of heat shock protein 70, TLR4, NOD1, NOD2, myeloid differentiation primary response gene 88, interleukin 1 receptor-associated kinase 1, TNF receptor-associated factor 6, receptor-interacting serine/threonine-protein kinase 2-like, nuclear factor-kappaB transcription factor P65 in the jejunum of piglets. Tryptophan alleviated LPS-induced necroptosis and decreased the mRNA expression of mixed lineage kinase domain-like, receptor-interacting serine/threonine kinase 1, receptor-interacting serine/threonine-protein kinase 3-like, Fas (TNFRSF6)-associated via death domain, PGAM family member 5. Collectively, our results suggest that tryptophan supplementation helps in the attenuation of intestinal injury and inflammation by alleviating necroptosis and TLR4/NOD in lipopolysaccharide-challenged pigs.

The Effect of Prebiotic Supplements on the Gastrointestinal Microbiota and Associated Health Parameters in Pigs

Establishing a balanced and diverse microbiota in the GIT of pigs is crucial for optimizing health and performance throughout the production cycle. The post-weaning period is a critical phase, as it is often associated with dysbiosis, intestinal dysfunction and poor performance. Traditionally, intestinal dysfunctions associated with weaning have been alleviated using antibiotics and/or antimicrobials. However, increasing concerns regarding the prevalence of antimicrobial-resistant bacteria has prompted an industry-wide drive towards identifying natural sustainable dietary alternatives. Modulating the microbiota through dietary intervention can improve animal health by increasing the production of health-promoting metabolites associated with the improved microbiota, while limiting the establishment and proliferation of pathogenic bacteria. Prebiotics are a class of bioactive compounds that resist digestion by gastrointestinal enzymes, but which can still be utilized by beneficial microbes within the GIT. Prebiotics are a substrate for these beneficial microbes and therefore enhance their proliferation and abundance, leading to the increased production of health-promoting metabolites and suppression of pathogenic proliferation in the GIT. There are a vast range of prebiotics, including carbohydrates such as non-digestible oligosaccharides, beta-glucans, resistant starch, and inulin. Furthermore, the definition of a prebiotic has recently expanded to include novel prebiotics such as peptides and amino acids. A novel class of -biotics, referred to as "stimbiotics", was recently suggested. This bioactive group has microbiota-modulating capabilities and promotes increases in short-chain fatty acid (SCFA) production in a disproportionally greater manner than if they were merely substrates for bacterial fermentation. The aim of this review is to characterize the different prebiotics, detail the current understating of stimbiotics, and outline how supplementation to pigs at different stages of development and production can potentially modulate the GIT microbiota and subsequently improve the health and performance of animals.

The Effect of Maternal Probiotic or Synbiotic Supplementation on Sow and Offspring Gastrointestinal Microbiota, Health, and Performance

The increasing prevalence of antimicrobial-resistant pathogens has prompted the reduction in antibiotic and antimicrobial use in commercial pig production. This has led to increased research efforts to identify alternative dietary interventions to support the health and development of the pig. The crucial role of the GIT microbiota in animal health and performance is becoming increasingly evident. Hence, promoting an improved GIT microbiota, particularly the pioneer microbiota in the young pig, is a fundamental focus. Recent research has indicated that the sow's GIT microbiota is a significant contributor to the development of the offspring's microbiota. Thus, dietary manipulation of the sow's microbiota with probiotics or synbiotics, before farrowing and during lactation, is a compelling area of exploration. This review aims to identify the potential health benefits of maternal probiotic or synbiotic supplementation to both the sow and her offspring and to explore their possible modes of action. Finally, the results of maternal sow probiotic and synbiotic supplementation studies are collated and summarized. Maternal probiotic or synbiotic supplementation offers an effective strategy to modulate the sow's microbiota and thereby enhance the formation of a health-promoting pioneer microbiota in the offspring. In addition, this strategy can potentially reduce oxidative stress and inflammation in the sow and her offspring, enhance the immune potential of the milk, the immune system development in the offspring, and the sow's feed intake during lactation. Although many studies have used probiotics in the maternal sow diet, the most effective probiotic or probiotic blends remain unclear. To this extent, further direct comparative investigations using different probiotics are warranted to advance the current understanding in this area. Moreover, the number of investigations supplementing synbiotics in the maternal sow diet is limited and is an area where further exploration is warranted.

Gastrointestinal digestibility insights of different levels of coated complex trace minerals supplementation on growth performance of yellow-feathered broilers

This study was designed to evaluate the optimum additional level of coated complex trace minerals (TMs) and its impacts on the growth performance of broilers through measurement of digestibility of nutrients and intestinal development. In a 56-day trial, a total of 360 one-day-old male yellow-feathered broilers were randomly divided into six dietary treatment groups. Each treatment contained six replicates, with 10 birds. The control group was supplemented with 1,000 mg/kg of uncoated complex TMs in the basal diet (UCCTM1000). The remaining 5 treatments were degressively supplemented with coated complex TMs from 1,000 to 200 mg/kg in the basal diet, which were considered as (CCTM1000), (CCTM800), (CCTM600), (CCTM400), (CCTM200), respectively. Results: On comparing the UCCTM1000 supplementation, the CCTM1000 supplementation decreased the feed to gain ratio (F/G) (P < 0.05), increased digestibility of crude protein (CP) (P < 0.05), crude fat (CF) (P < 0.05), villus height (VH) of duodenum (P < 0.05), and the mRNA expression level of occludin in jejunal mucosa (P < 0.05). In addition, the F/G was lower in the CCTE600 group than that in the CCTE200 group (P < 0.05). The VH to crypt depth (CD) ratio (V/C) of jejunum and ileum in the CCTM400 and CCTM600 groups was higher (P < 0.05) than that in the CCTM1000 group. The serum endotoxin and D-lactate level and CP digestibility were increased by dietary coated complex TMs addition level. The mRNA expression levels of claudin-1 and ZO-1 in the CCTM600 group were higher (P < 0.05) than that in the CCTM1000 group. In conclusion, adding 600 mg/kg of coated complex TMs showed the minimum F/G and the maximum crude protein digestibility and intestine development of yellow-feathered broilers compared with other treatments. This supplementation level of coated complex TMs could totally replace 1,000 mg/kg of uncoated complex TMs to further decrease the dose of TMs and raise economic benefit.

Tryptophan Supplementation Enhances Intestinal Health by Improving Gut Barrier Function, Alleviating Inflammation, and Modulating Intestinal Microbiome in Lipopolysaccharide-Challenged Piglets

Tryptophan (Trp) can modify the gut microbiota. However, there is no information about the effect of Trp on intestinal microbiota after lipopolysaccharide (LPS) challenge. This study aimed to investigate the effect of Trp on intestinal barrier function, inflammation, antioxidant status, and microbiota in LPS-challenged piglets. A total of 18 weaned castrated piglets were randomly divided into three treatments with 6 replicate per treatment, namely, (i) non-challenged control (CON); (ii) LPS-challenged control (LPS-CON); and (iii) LPS + 0.2% Trp (LPS-Trp). After feeding with control or 0.2% tryptophan-supplemented diets for 35 days, pigs were intraperitoneally injected with LPS (100 μg/kg body weight) or saline. At 4 h post-challenge, all pigs were slaughtered, and colonic samples were collected. The samples were analyzed for gut microbiota, fatty acids, antioxidant parameters, and the expression of mRNA and protein. The community bar chart showed that Trp supplementation to LPS-challenged pigs increased the relative abundance of Anaerostipes (P < 0.05) and tended to increase the relative abundance of V9D2013_group (P = 0.09), while decreased the relative abundance of Corynebacterium (P < 0.05) and unclassified_c__Bacteroidia (P < 0.01). Gas chromatography showed that Trp increased the concentrations of acetate, propionate, butyrate, and isovalerate in the colonic digesta (P < 0.05). Trp reduced the mRNA level of pro-inflammatory cytokines (P < 0.01), and increased mRNA level of aryl hydrocarbon receptor, cytochrome P450 (CYP) 1A1 and CYP1B1 (P < 0.05). Correlation analysis results showed that acetate, propionate, and butyrate concentrations were positively correlated with mRNA level of occludin and CYP1B1 (P < 0.05), and were negatively correlated with pro-inflammatory cytokines gene expression (P < 0.05). Isovalerate concentration was positively correlated with catalase activity (P < 0.05), and was negatively correlated with pro-inflammatory cytokines gene expression (P < 0.05). Furthermore, Trp enhanced the antioxidant activities (P < 0.01), and increased mRNA and protein expressions of claudin-1, occludin, and zonula occludens-1 (P < 0.01) after LPS challenge. These results suggest that Trp enhanced intestinal health by a modulated intestinal microbiota composition, improved the short chain fatty acids synthesis, reduced inflammation, increased antioxidant capacity, and improved intestinal barrier function.

Effects of Zinc Oxide Nanoparticles on Growth, Intestinal Barrier, Oxidative Status and Mineral Deposition in 21-Day-Old Broiler Chicks

This experiment was to study the effects of zinc oxide nanoparticles (ZnO-NPs) on growth, intestinal barrier, oxidative status, and mineral deposition. In total, 256 one-day-old chicks were randomly allotted to 4 dietary groups and fed with basal diet plus 80 mg/kg ZnSO₄ (ZnSO₄ group) or plus 40, 80, and 160 mg/kg ZnO-NPs, respectively, for 21 days. Compared with the ZnSO₄ group, dietary 40, 80, and 160 mg/kg ZnO-NPs did not alter growth (average daily gain, body weight, and gain to feed ratio), and serum activities of glutamic-pyruvic transaminase, alkaline phosphatase and glutamic oxalacetic transaminase (P > 0.05). However, dietary 80 and 160 mg/kg ZnO-NPs linearly decreased serum D-lactate content and diamine oxidase activity (P < 0.01). Moreover, 80 mg/kg ZnO-NPs enhanced zonula occludens-1 (ZO-1) mRNA expression in jejunal mucosa (P = 0.02). Dietary ZnO-NPs increased total antioxidant capacity activity (P = 0.01), and 80 mg/kg ZnO-NPs decreased malondialdehyde content in jejunal mucosa as compared to the ZnSO₄ group (P = 0.02). In contrast, dietary ZnO-NPs did not alter mRNA expressions of superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, heme oxygennase-1 (HO-1) and NAD (P)H: quinone oxidoreductase 1 (NQO1) (P > 0.05). No significant difference was found in selected mineral concentrations (Mn, Cu, Fe and Zn) in the liver among ZnSO₄ and 3 ZnO-NP groups (P > 0.05). However, 160 mg/kg ZnO-NPs increased fecal contents of Zn, Fe and Cu (P < 0.01), but did not affect fecal Mn level (P > 0.05). Therefore, results suggested that ZnO-NPs could be an additive to enhance the intestinal barrier and antioxidant capacity of broiler chicks, whereas the inclusion of 80 mg/kg would be more efficient.

Enhanced Intestinal Barriers by Puerarin in Combination with Tryptophan

The intestinal barrier is essential for maintaining human intestinal health. The growing number of studies has shown that both puerarin and tryptophan and its metabolites have a beneficial effect on the intestinal barrier. This study aims at the combination of puerarin and tryptophan or its metabolites for improving the intestinal barrier. In our study, 40 female Sprague-Dawley rats were randomly divided into five groups (n = 8) for a 4-week experiment and dextran sodium sulfate was used to induce an intestinal barrier injury in rats. Our results showed that puerarin combined with tryptophan or its metabolites (indole-3-propionic acid, IPA) improved the intestinal barrier by enhancing the mucus layer barrier, which was mainly achieved by increasing the number of goblet cells and promoting the secretion of MUC2. Both TRPM5 and VAMP8 promoted MUC2 secretion in goblet cells through exocytosis, but their mechanisms of action are different. In our study, we found that puerarin and tryptophan showed different effects on TRPM5 and VAMP8, respectively. Puerarin enhances the expression of TRPM5, and tryptophan inhibits the expression of TRPM5; however, puerarin and tryptophan have no significant effect on the expression of VAMP8.

New Insights Into Gut-Bacteria-Derived Indole and Its Derivatives in Intestinal and Liver Diseases

The interaction between host and microorganism widely affects the immune and metabolic status. Indole and its derivatives are metabolites produced by the metabolism of tryptophan catalyzed by intestinal microorganisms. By activating nuclear receptors, regulating intestinal hormones, and affecting the biological effects of bacteria as signaling molecules, indole and its derivatives maintain intestinal homeostasis and impact liver metabolism and the immune response, which shows good therapeutic prospects. We reviewed recent studies on indole and its derivatives, including related metabolism, the influence of diets and intestinal commensal bacteria, and the targets and mechanisms in pathological conditions, especially progress in therapeutic strategies. New research insights into indoles will facilitate a better understanding of their druggability and application in intestinal and liver diseases.

Dietary glucose oxidase and/or catalase supplementation alleviates intestinal oxidative stress induced by diquat in weaned piglets

This study investigated the effects of dietary exogenous glucose oxidase (GOD) and/or catalase (CAT) on the intestinal antioxidant capacity and barrier function in piglets under oxidative stress. Sixty pigs assigned randomly to five treatment groups-CON: basal diet; DIQ: basal diet; GOD: basal diet + 40-U GOD/kg diet; CAT: basal diet + 50-U CAT/kg diet; and GC: basal diet + 40-U GOD/kg diet + 50-U CAT/kg diet-were analyzed. On Day 14, the CON group was injected with saline, and the others were treated with diquat. The results showed that in diquat-treated piglets, supplementation of dietary GOD and CAT elevated the superoxide dismutase and CAT activities and attenuated the malondialdehyde level in plasma and intestinal mucosa, enhanced the duodenal villus height and villus height/crypt depth ratio, upregulated ZO-1 mRNA level, and attenuated the apoptosis of the epithelial cells and caspase-3 mRNA level in the intestine. Additionally, the supplementation upregulated mRNA expression of the intestinal NF-E2-related factor 2-regulated genes in diquat-treated piglets. However, GOD combined with CAT could not alleviate oxidative damage better than supplementation of CAT or GOD alone under oxidative stress. Overall, the study provides a potential alternative that could relieve the weaning stress in piglets and help formulate antibiotic-free diets.

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.

Effects of Coated Cysteamine on Oxidative Stress and Inflammation in Weaned Pigs

This study aimed to explore the effects of dietary coated cysteamine on oxidative stress and inflammation in diquat-induced weaning pigs. Twenty-four pigs were randomly assigned to three dietary groups with eight replicates: the control (fed base diet), diquat (fed base diet), and coated cysteamine + diquat groups (fed 80 mg/kg cysteamine). The experiment was conducted for 21 d, and consisted of a pre-starter period (14 d) and a starter period (7 d). Coated cysteamine treatment significantly increased (p < 0.05) the final weight and average daily gain (ADG) in pigs. The contents of alkaline phosphatase (ALP), immunoglobulin G (IgG), serine (Ser), and isoleucine (Ile) were elevated (p < 0.05) while the contents of albumin (ALB) and aspartic acid (Asp) were reduced (p < 0.05) in the serum after coated cysteamine supplementation. Coated cysteamine supplementation resulted in greater (p < 0.05) serum superoxide dismutase (SOD) activity, the expression of interleukin-10 (IL-10) mRNA in the colon, and the CuSOD mRNA expression in the jejunum (p < 0.05) and colon (p = 0.073). Coated cysteamine supplementation showed an increasing trend in villus height (p = 0.060), villus height/crypt depth (V/C) (p = 0.056), the expression levels of zonula occludens-1 (ZO-1) mRNA (p = 0.061), and Occludin mRNA (p = 0.074) in the jejunum. In summary, dietary supplementation with coated cysteamine improves the intestinal barrier function of the jejunum by increasing the immunoglobulin content and the relative expression of intestinal immune factor mRNA in pigs while alleviating oxidative stress and inflammatory reactions caused by diquat.

Research Progress on Oxidative Stress and Its Nutritional Regulation Strategies in Pigs

Oxidative stress refers to the dramatic increase in the production of free radicals in human and animal bodies or the decrease in the ability to scavenging free radicals, thus breaking the antioxidation-oxidation balance. Various factors can induce oxidative stress in pig production. Oxidative stress has an important effect on pig performance and healthy growth, and has become one of the important factors restricting pig production. Based on the overview of the generation of oxidative stress, its effects on pigs, and signal transduction pathways, this paper discussed the nutritional measures to alleviate oxidative stress in pigs, in order to provide ideas for the nutritional research of anti-oxidative stress in pigs.

Ameliorative Effect of Dietary Tryptophan on Neurodegeneration and Inflammation in d-Galactose-Induced Aging Mice with the Potential Mechanism Relying on AMPK/SIRT1/PGC-1α Pathway and Gut Microbiota

Dietary tryptophan affects intestinal homeostasis and neurogenesis, whereas the underlying mechanism and the reciprocal interaction between tryptophan and gut microbiota in aging are unclear. This investigation was performed to determine the effect and mechanism of tryptophan on intestinal- and neuro- health in aging. In present study, the 0.4% tryptophan diet significantly ameliorated the oxidative stress and inflammation in the aging mice, potentially through the regulation of 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) and nuclear factor κB (NF-κB) pathways. The 0.4% tryptophan diet increased the levels of indoles in colon contents, which indicated the potential contribution of tryptophan metabolites. Microbiome analysis revealed that the 0.4% tryptophan diet raised the relative abundance of Akkermansia in aging. The ameliorated effect of 0.4% tryptophan on neurodegeneration and neuroinflammation was summarized to potentially rely on the brain-derived neurotrophic factor- (BDNF) and NF-κB-related pathways. These findings provide the research evidence for the beneficial effect of tryptophan on aging.

Invited Review: Maintain or Improve Piglet Gut Health around Weanling: The Fundamental Effects of Dietary Amino Acids

Gut health has significant implications for swine nutrient utilization and overall health. The basic gut morphology and its luminal microbiota play determinant roles for maintaining gut health and functions. Amino acids (AA), a group of essential nutrients for pigs, are not only obligatory for maintaining gut mucosal mass and integrity, but also for supporting the growth of luminal microbiota. This review summarized the up-to-date knowledge concerning the effects of dietary AA supplementation on the gut health of weanling piglets. For instance, threonine, arginine, glutamine, methionine and cysteine are beneficial to gut mucosal immunity and barrier function. Glutamine, arginine, threonine, methionine and cysteine can also assist with relieving the post-weaning stress of young piglets by improving gut immunological functions, antioxidant capacity, and/or anti-inflammatory ability. Glutamine, glutamate, glycine and cysteine can assist to reconstruct the gut structure after its damage and reverse its dysfunction. Furthermore, methionine, lysine, threonine, and glutamate play key roles in affecting bacteria growth in the lumen. Overall, the previous studies with different AA showed both similar and different effects on the gut health, but how to take advantages of all these effects for field application is not clear. It is uncertain whether these AA effects are synergetic or antagonistic. The interactions between the effects of non-nutrient feed additives and the fundamental effects of AA warrant further investigation. Considering the global push to minimize the antibiotics and ZnO usage in swine production, a primary effort at present may be made to explore the specific effects of individual AA, and then the concert effects of multiple AA, on the profile and functions of gut microbiota in young pigs.

Porcine colonoids and enteroids keep the memory of their origin during regeneration

The development of alternative in vitro culture methods has increased in the last decade as three-dimensional organoids of various tissues, including those of the small and large intestines. Due to their multicellular composition, organoids offer advantages over traditionally used immortalized or primary cell lines. However, organoids must be accurate models of their tissues of origin. This study compared gene expression profiles with respect to markers of specific cell types (stem cells, enterocytes, goblet, and enteroendocrine cells) and barrier maturation (tight junctions) of colonoid and enteroid cultures with their tissues of origin and colonoids with enteroids. Colonoids derived from three healthy pigs formed multilobed structures with a monolayer of cells similar to the crypt structures in colonic tissue. Colonoid and enteroid gene expression signatures were more similar to those found for the tissues of their origin than to each other. However, relative to their derived tissues, organoids had increased gene expression levels of stem cell markers Sox9 and Lgr5 encoding sex-determining region Y-box 9 and leucine-rich repeat-containing G protein-coupled rector 5, respectively. In contrast, expression levels of Occl and Zo1 encoding occludin and zonula occludens 1, respectively, were decreased. Expression levels of the cell lineage markers Atoh1, Cga, and Muc2 encoding atonal homolog 1, chromogranin A, and mucin 2, respectively, were decreased in colonoids, whereas Sglt1 and Apn encoding sodium-glucose transporter 1 and aminopeptidase A, respectively, were decreased in enteroids. These results indicate colonoid and enteroid cultures were predominantly comprised of undifferentiated cell types with decreased barrier maturation relative to their tissues of origin.

Dietary Tryptophan Levels Impact Growth Performance and Intestinal Microbial Ecology in Weaned Piglets via Tryptophan Metabolites and Intestinal Antimicrobial Peptides

Tryptophan (Trp) plays an important role in piglet growth. However, the effect of dietary Trp on microbial flora is still poorly understood. A total of 40 28-d weaned piglets were allocated to four groups with 10 barrows per group and one pig per replicate. Piglets were fed a corn and soybean meal-based diet with 0.14%, 0.21%, 0.28%, or 0.35% Trp for four weeks. Five piglets from each diet group were euthanized, and blood and tissue samples were collected. The average daily body weight gain, average daily feed intake, feed conversion ratio, spleen index, pancreas index, longissimus dorsi muscle index, plasma insulin, 5-hydroxytryptamine, kynurenine, and Trp concentrations of weaned piglets increased in a dose-dependent manner (p < 0.05). Compared with the 0.14% Trp diet, the adequate-Trp diets (0.21%, 0.28%, or 0.35%) down-regulated the relative abundances of 12 genera including Turicibacter, Prevotella, Mitsuokella, Anaerovibrio, Megasphaera, Succinivibrio, Sutterella, Desulfovibrio, and Methanobrevibacter (p < 0.05); up-regulated the abundances of Ruminococcaceae, Lactobacillus, and Muribaculaceae in the colon (p < 0.05); and augmented the mRNA level and concentration of porcine β-defensin 2 in the small intestinal mucosa (p < 0.05). Moreover, Trp-adequate diets increased the abundances of Trp hydroxylase, indoleamine 2,3-dioxygenase, porcine β-defensin 2, phosphorylated mammalian target of rapamycin, and phosphorylated protein kinase B in the small intestinal mucosa (p < 0.05). We noted that a corn and soybean meal-based diet with 0.35% Trp may be a nutritional strategy to improve growth performance, intestinal mucosal barrier integrity, and intestinal microbial ecology in weaned piglets.

Indole-3-propionic Acid Improved the Intestinal Barrier by Enhancing Epithelial Barrier and Mucus Barrier

Destruction in intestinal barrier is concomitant with the intestinal diseases. There is growing evidence that tryptophan-derived intestinal bacterial metabolites play a critical role in maintaining the balance of intestinal mucosa. In this study, the Caco-2/HT29 coculture model was used to evaluate the effect of indole-3-propionic acid (IPA) on the intestinal barrier and explore its underlying mechanism. We found that IPA increased transepithelial electrical resistance and decreased paracellular permeability which was consistent with the increase in tight junction proteins (claudin-1, occludin, and ZO-1). Furthermore, IPA strengthened the mucus barrier by increasing mucins (MUC2 and MUC4) and goblet cell secretion products (TFF3 and RELMβ). Additionally, IPA weakened the expression of LPS-induced inflammatory factors. These discoveries provide new views for understanding the improvement of intestinal barrier by gut microbial metabolites of aromatic amino acids.

Tryptophan Attenuates the Effects of OTA on Intestinal Morphology and Local IgA/IgY Production in Broiler Chicks

Ochratoxin A (OTA) is a mycotoxin produced by species of Penicillium and Aspergillus that can contaminate products of plant origin that are used as animal feed. Through oral exposure, this mycotoxin primarily affects the chicken gastrointestinal system. The present study evaluated the intestinal toxic effects of OTA and the introduction of L-tryptophan to alleviate these effects in chickens. One-day-old chicks were exposed to a single OTA dose (1.4 mg/kg body weight—b.w.) and treated with or without four daily doses of L-tryptophan (100 mg/kg b.w.). Duodenal villus height/crypt depth, fecal immunoglobulin A/immunoglobulin Y (IgA/IgY) levels, and duodenal positive immunoglobulin A cells (IgA⁺) were evaluated by histology, ELISA, and immunohistochemistry, respectively, on the 14th day. There were significant changes in the duodenal villus height, crypt depth, and levels of fecal IgA/IgY and duodenal IgA⁺ cells (p < 0.05) in groups exposed to OTA. On the other hand, groups exposed to OTA and treated with L-tryptophan showed similar levels of villus height, IgA/IgY levels, and duodenal IgA⁺ cells to those of the control group (p > 0.05). In conclusion, exposure to a single dose of OTA orally induces changes in intestinal morphology, levels of IgA/IgY antibodies, and IgA⁺ cells. Thus, treatment with L-tryptophan may be a valid alternative means to reduce the harmful effects of OTA on the intestinal mucosa, which requires further study.

Effects of Dietary Histidine on Growth Performance, Serum Amino Acids, and Intestinal Morphology and Microbiota Communities in Low Protein Diet-Fed Piglets

Previous study showed that low protein diet-fed pigs are characterized by lower histidine concentration in the serum and muscle, suggesting that histidine may involve in protein-restricted response. Thus, the current study mainly investigated the effects of dietary histidine on growth performance, blood biochemical parameters and amino acids, intestinal morphology, and microbiota communities in low protein diet-challenged-piglets. The results showed that protein restriction inhibited growth performance, blood biochemical parameters and amino acids, and gut microbiota but had little effect on intestinal morphology. Dietary supplementation with histidine markedly enhanced serum histidine level and restored tryptophan concentration in low protein diet-fed piglets, while growth performance and intestinal morphology were not markedly altered in histidine-treated piglets. In addition, histidine exposure failed to affect bacterial diversity (observed species, Shannon, Simpson, Chao1, ACE, and phylogenetic diversity), but histidine-treated piglets exhibited higher abundances of Butyrivibrio and Bacteroides compared with the control and protein-restricted piglets. In conclusion, dietary histidine in low protein diet enhanced histidine concentration and affected gut microbiota (Butyrivibrio and Bacteroides) but failed to improve growth performance and intestinal morphology.

Modulation of Crustacean Innate Immune Response by Amino Acids and Their Metabolites: Inferences From Other Species

Aquaculture production of crustaceans (mainly shrimp and crabs) has expanded globally, but disease outbreaks and pathogenic infections have hampered production in the last two decades. As invertebrates, crustaceans lack an adaptive immune system and mainly defend and protect themselves using their innate immune system. The immune system derives energy and metabolites from nutrients, with amino acids constituting one such source. A growing number of studies have shown that amino acids and their metabolites are involved in the activation, synthesis, proliferation, and differentiation of immune cells, as well as in the activation of immune related signaling pathways, reduction of inflammatory response and regulation of oxidative stress. Key enzymes in amino acid metabolism have also been implicated in the regulation of the immune system. Here, we reviewed the role played by amino acids and their metabolites in immune-modulation in crustaceans. Information is inferred from mammals and fish where none exists for crustaceans. Research themes are identified and the relevant research gaps highlighted for further studies.

Impacts of Amino Acids on the Intestinal Defensive System

The intestine interacts with a diverse community of antigens and bacteria. To keep its homeostasis, the gut has evolved with a complex defense system, including intestinal microbiota, epithelial layer and lamina propria. Various factors (e.g., nutrients) affect the intestinal defensive system and progression of intestinal diseases. This review highlights the current understanding about the role of amino acids (AAs) in protecting the intestine from harm. Amino acids (e.g., arginine, glutamine and tryptophan) are essential for the function of intestinal microbiota, epithelial cells, tight junction, goblet cells, Paneth cells and immune cells (e.g., macrophages, B cells and T cells). Through the modulation of the intestinal defensive system, AAs maintain the integrity and function of the intestinal mucosa and inhibit the progression of various intestinal diseases (e.g., intestinal infection and intestinal colitis). Thus, adequate intake of functional AAs is crucial for intestinal and whole-body health in humans and other animals.

Regulation of the intestinal barrier by nutrients: The role of tight junctions

Tight junctions (TJs) play an important role in intestinal barrier function. TJs in intestinal epithelial cells are composed of different junctional molecules, such as claudin and occludin, and regulate the paracellular permeability of water, ions, and macromolecules in adjacent cells. One of the most important roles of the TJ structure is to provide a physical barrier to luminal inflammatory molecules. Impaired integrity and structure of the TJ barrier result in a forcible activation of immune cells and chronic inflammation in different tissues. According to recent studies, the intestinal TJ barrier could be regulated, as a potential target, by dietary factors to prevent and reduce different inflammatory disorders, although the precise mechanisms underlying the dietary regulation remain unclear. This review summarizes currently available information on the regulation of the intestinal TJ barrier by food components.

Dietary Puerarin Supplementation Alleviates Oxidative Stress in the Small Intestines of Diquat-Challenged Piglets

Simple Summary

The oxidant stress which piglets suffer from during the weaning period has caused huge losses to the pig farm industry. It is important for scientists to find an effective way to alleviate the oxidant stress in weaned piglets. This study was designed to test the hypothesis that dietary puerarin supplementation alleviates oxidative stress in the small intestine of diquat-challenged piglets. Interestingly, dietary puerarin supplementation improved intestinal morphology, cell proliferation, barrier function, and increased Nrf2 and its downstream enzymes in diquat-challenged piglets, which shows that puerarin has potent protective effects against diquat-induced oxidative stress. These findings will be very beneficial to the pig industry, especially to the development of antibiotic-free diets, new anti-inflammatory drugs and the application of puerarin in piglets.

Abstract

This study was conducted to demonstrate that dietary puerarin supplementation alleviates oxidative stress in the small intestine of diquat-challenged piglets. The results showed that puerarin administration markedly alleviated diquat-induced intestinal injury, which was indicated by the improvement of intestinal morphology, cell proliferation and barrier function. One of the potential mechanisms responsible for this was the decrease in oxidative stress, as evidenced by the increase in activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and total antioxidant capacity (T-AOC) in the small intestine. Puerarin increased the protein expression levels of NF-E2-related factor 2 (Nrf2) and its downstream enzymes, including heme oxygenase 1 (HO-1), glutamate–cysteine ligase catalytic and its modifier subunit (GCLc and GCLm) in the jejunal mucosa of diquat-induced piglets. Puerarin administration improved intestinal morphology, cell proliferation, and barrier function, and increased Nrf2 and its downstream enzymes. These findings indicate that the dietary supplementation of puerarin attenuates the oxidative stress involving Nrf2 signaling pathways in diquat-challenged piglets.

Effects of early protein restriction on the growth performance and gut development of pigs fed diets with or without antibiotic

In the livestock husbandry compensatory growth may be explored as a means to improve nutrient utilization, to reduce gut health problems due to excess protein intake, to simplify feeding strategies and thus to improve production efficiencies. This study investigated the effects of early protein restriction (EPR) and early antibiotic intervention (EAI) on growth performance, intestinal morphology, colonic bacteria, metabolites and mucosal gene expressions during the restriction phase and re-alimentation phase. A total of 64 piglets (10.04 ± 0.73 kg) were randomly divided into four treatment groups according to a 2 × 2 factorial arrangement with two levels of proteins (14% v. 20%) and two levels of antibiotics (0 v. 50 mg/kg kitasamycin and 20 mg/kg colistin sulphate). After a 30-day restriction phase with four kinds of diets, all groups were fed the same diets for another 74 days. The results showed that EPR decreased BW, average daily gain (ADG), average daily feed intake in the restriction phase (P < 0.01) and increased ADG on days 66 to 104 of the late re-alimentation phase. Early protein restriction could decrease the villus height in the jejunum (P < 0.05), while shifting to the same diets restored the villus height. Meanwhile, during the re-alimentation phase, pigs in the protein restriction groups had increased concentrations of total short chain fatty acids (P < 0.05), and modified the abundances of Firmicutes and Bacteroidetes in the colon. Furthermore, the lower microbial diversity caused by EPR was improved, and gene expression analysis indicated a better barrier function in the colon. During the whole trial, EAI had no interaction with EPR and played a dispensable role in compensatory growth. Collectively, the retardation of growth caused by EPR can be compensated for in the later stages of pig raising, and accompanied by altered intestinal morphology, microbial composition.

Tight Junction Proteins in the Weaned Piglet Intestine: Roles and Regulation

The intestinal epithelial barrier plays a crucial role in the health and growth of weaned piglets. Proper epithelial function mainly depends on tight junctions (TJs), which act as both ion channels and a barrier against noxious molecules. TJs are multiprotein complexes consisting of transmembrane and membrane-associated proteins. Because the intestine in piglets is immature and incomplete, its structure and function are easily impaired by various stresses, infections, and food-related factors. Certain nutrients have been demonstrated to participate in intestinal TJ regulation. Probiotics, amino acids, fibers, oligosaccharide, and certain micronutrients can enhance barrier integrity and counteract infections through elevated TJ protein expression and distribution. In this review, the distribution and classification of intestinal TJs is described, the factors influencing TJs after weaning are summarized, and the regulation of weaning piglet intestinal TJs by nutrients is discussed.

Protein restriction and succedent realimentation affecting ileal morphology, ileal microbial composition and metabolites in weaned piglets

Dietary protein restriction is one of the effective ways to reduce post-weaning diarrhoea and intestinal fermentation in piglets, but it may also reduce growth performance. The compensatory growth induced by subsequent protein realimentation may solve the issue. However, little research has been done on the impact of protein realimentation on the gut. In this study, the effects of protein restriction and realimentation on ileal morphology, ileal microbial composition and metabolites in weaned piglets were investigated. Thirty-six 28-day-old weaned piglets with an average body weight of 6.47 ± 0.04 kg were randomly divided into a control group and a treatment group. The CP level in the diet of the control group was 18.83% for the entire experimental period. The piglets in the treatment group were fed 13.05% CP between days 0 and 14 and restored to a diet of 18.83% CP for days 14 to 28. On day 14 and 28, six pigs from each group were sacrificed and sampled. It was found that the abundance of Lactobacillus and Salmonella in the ileal digesta was significantly lower in the treatment group than the control group on day 14, whereas the abundance of Clostridium sensu stricto 1, Streptococcus, Halomonas and Pseudomonas significantly increased in the ileal digesta of the treatment group on day 14 compared with the control group. In addition, reduced concentrations of lactic acid, total short-chain fatty acids (total SCFAs), total branched chain fatty acids, ammonia and impaired ileal morphology and mucosal barrier were observed in the treatment group on day 14. However, diarrhoea levels decreased in the treatment group throughout the experiment. During the succedent protein realimentation stage, the treatment group demonstrated compensatory growth. Compared with the control group, the treatment group showed increased abundance of Lactobacillus and reduced abundance of Salmonella, Halomonas and Pseudomonas in the ileum on day 28. The concentrations of lactic acid and total SCFAs increased significantly, whereas the concentration of ammonia remained at a lower level in the treatment group on day 28 compared with the control group. Overall, protein realimentation could improve ileal morphology and barrier functions and promote ileal digestive and absorptive functions. In conclusion, ileal microbial composition and metabolites could change according to dietary protein restriction and realimentation and eventually influence ileal morphology and barrier functions.

Succinate Modulates Intestinal Barrier Function and Inflammation Response in Pigs

Succinate is a metabolic intermediate of the tricarboxylic acid (TCA) cycle in all aerobic organisms, and is also a vital microbial metabolite in the gut. Although succinate is known to regulate intestinal metabolism and immune function, its role in the protection of the intestinal epithelial barrier function and inflammation is poorly characterized. In this study, we evaluated the effects of succinate on intestinal epithelial barrier function and inflammation in pigs. Twenty-four growing pigs were distributed into three groups (n = 8) and received either a basal diet (control group) or the same diet supplemented with 0.1% succinate or 1% succinate. The diet supplemented with 1% succinate led to alterations in the intestinal morphology. We confirmed in vitro that 5 mM succinate treatment modulated intestinal epithelial permeability by increased transepithelial electrical resistance (TEER) in intestinal porcine epithelial cell (IPEC)-J2 cells. Furthermore, succinate treatment increased the abundance of tight junction proteins claudin-1, zona occluden (ZO)-1, and ZO-2 in the jejunum in vivo and in vitro. In addition, dietary succinate supplementation promoted the expression of inflammatory cytokines interleukin (IL)-25, IL-10, IL-8, and IL-18 in the jejunum. Taken together, these data identify a novel role of succinate in the modulation of intestinal epithelial barrier function, which may be a nutritional target to improve gut health in animals.

Indoleamine-pyrrole 2,3-dioxygenase-1 (IDO-1) mRNA is over-expressed in the duodenal mucosa and is negatively correlated with serum tryptophan concentrations in dogs with protein-losing enteropathy

INTRODUCTION

Dogs with protein-losing enteropathy (PLE) have decreased serum tryptophan concentrations, which may contribute to disease pathogenesis. Indoleamine-pyrrole 2,3-dioxygenase-1 (IDO-1) expression is associated with low serum tryptophan concentrations and is increased in the gastrointestinal tract of humans with inflammatory bowel disease (IBD). Therefore, the objective of our study was to determine if the mRNA expression of IDO-1 is increased in the duodenal mucosa of dogs with PLE as compared to dogs with chronic enteropathy (CE) and healthy dogs, and whether this expression is correlated with changes in serum tryptophan concentration.

METHODS

Our study was a retrospective study using archived paraffin-embedded duodenal biopsy specimens from 8 healthy Beagle dogs from the Iowa State University Canine Service Colony and 18 and 6 client-owned dogs diagnosed with CE and PLE, respectively at the Bristol Veterinary School. A novel RNA in situ hybridization (ISH) technology, RNAscope, was used to identify IDO-1 mRNA mucosal expression in duodenal tissues. An IDO-1 specific probe was hybridized onto 10 duodenal biopsy sections from each dog whereby RNAscope signal (mRNA expression) was quantified by a single operator using light microscopy.

RESULTS

Dogs with PLE had significantly higher mRNA expression of IDO-1 in the duodenal mucosa compared to healthy dogs (mucosal percentage IDO-1 positive: P = 0.0093, (mean ± S.D) control: 19.36 ± 7.08, PLE: 34.12 ± 5.98, average fold difference: 1.76 and mucosal IDO-1 H-score: P = 0.0356, (mean ± S.D) control: 45.26 ± 19.33, PLE: 84.37 ± 19.86, average fold difference: 1.86). The duodenal mucosal mRNA expression of IDO-1 was negatively correlated with serum tryptophan concentrations in dogs with PLE (mucosal IDO-1 H-score: Spearman's rank correlation coefficient = -0.94, P = 0.0048).

CONCLUSIONS

In conclusion, our study suggests that decreased serum tryptophan concentrations in dogs with PLE is associated with increased intestinal IDO-1 expression. Further studies are needed to determine potential inflammatory pathways responsible for increased expression of IDO-1 in the intestinal tract of dogs with PLE.

Histological and Comparative Transcriptome Analyses Provide Insights into Small Intestine Health in Diarrheal Piglets after Infection with Clostridium Perfringens Type C

C. perfringens type C can induce enteritis accompanied by diarrhea and annually causes significant economic losses to the global pig industry. The pathogenic mechanisms of C. perfringens type C in pigs are still largely unknown. To investigate this, we challenged seven-day-old piglets with C. perfringens type C to cause diarrhea. We performed hematoxylin & eosin (H&E) staining of the small intestine (including duodenum, jejunum, and ileum) and assessed gene expression in the ileal tissue. H&E staining of the duodenum, jejunum, and ileum demonstrated inflammation and edema of the lamina propria and submucosa. A total of 2181 differentially expressed genes (DEGs) were obtained in ileal tissues. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis of DEGs indicated that the main pathways were enriched in the T cell receptor signaling pathway, NF-kappa B signaling pathway, and (tumor necrosis factor) TNF signaling pathway. These results provide insights into the pathogenicity of C. perfringens type C and improve our understanding of host-bacteria interactions.

L-tryptophan Enhances Intestinal Integrity in Diquat-Challenged Piglets Associated with Improvement of Redox Status and Mitochondrial Function

Simple Summary

In the present study, three groups of piglets were treated with diquat, a bipyridyl herbicide which can utilize molecular oxygen to generate superoxide anion radicals and is widely considered as an effective chemical agent for inducing oxidative stress. The three groups were fed a 0, 0.15%, and 0.30% tryptophan (Trp) supplemented diet, and one control group without diquat treatment was used to study the protective effects of supplemented Trp on growth performance and intestinal barrier function of piglets exposed to oxidative stress. The results showed that 0.15% Trp supplementation alleviated diquat-induced impaired growth performance, intestinal barrier injury, redox imbalance, and mitochondrial dysfunction. These findings from the current study suggest that piglets under the condition of stress might need more Trp to maintain intestinal integrity and optimal growth performance, but the proper dosage of Trp supplementation is needed to determine for different conditions or models.

Abstract

Tryptophan (Trp) supplementation has been shown to improve growth performance and enhance intestinal integrity in piglets. However, the effects of dietary Trp supplementation on the intestinal barrier function in piglets exposed to oxidative stress remain unknown. This study was conducted to evaluate whether dietary Trp supplementation can attenuate intestinal injury, oxidative stress, and mitochondrial dysfunction of piglets caused by diquat injection. Thirty-two piglets at 25 days of age were randomly allocated to four groups: (1) the non-challenged control; (2) diquat-challenged control; (3) 0.15% Trp-supplemented diet + diquat; (4) 0.30% Trp supplemented diet + diquat. On day seven, the piglets were injected intraperitoneally with sterilized saline or diquat (10 mg/kg body weight). The experiment lasted 21 days. Dietary supplementation with 0.15% Trp improved growth performance of diquat-challenged piglets from day 7 to 21. Diquat induced an increased intestinal permeability, impaired antioxidant capacity, and mitochondrial dysfunction. Although dietary supplementation with 0.15% Trp ameliorated these negative effects induced by diquat challenge that showed decreasing permeability of 4 kDa fluorescein isothiocyanate dextran, increasing antioxidant indexes, and enhancing mitochondrial biogenesis. Results indicated that dietary supplementation with 0.15% Trp enhanced intestinal integrity, restored the redox status, and improved the mitochondrial function of piglets challenged with diquat.

Rumen-Protected 5-Hydroxytryptophan Improves Sheep Melatonin Synthesis in the Pineal Gland and Intestinal Tract

BACKGROUND Based on the extensive biological effects of melatonin (MLT), it is beneficial to increase the MLT content in the bodies of animals at a specific physiological stage. This study was conducted to investigate the effect of a diet supplemented with rumen-protected (RP) 5-hydroxytryptophan (5-HTP) on the pineal gland and intestinal tract MLT synthesis of sheep. MATERIAL AND METHODS Eighteen Kazakh sheep were assigned randomly to 3 diet groups: control group (CT, corn-soybean meal basal diet), CT+111 group (111 mg/kg BW RP 5-HTP), and CT+222 group (222 mg/kg BW RP 5-HTP). The gene expressions of aromatic amino acid decarboxylase (AADC), arylalkylamine N-acetyltransferase (AA-NAT), hydroxyindole-O-methyltransferase (HIOMT), monoamine oxidase A (MAOA), and the intermediates of MLT synthesis were observed from the pineal gland and intestinal tract by the reverse transcription (RT)-PCR method. The 5-HTP, 5-HT, N-acetylserotonin (NAS), MLT, and 5-hydroxyindole acetic acid (5-HIAA) contents in the pineal gland and intestinal tract were analyzed by ultra-high-performance liquid chromatography-tandem mass spectrometry. RESULTS The study showed that the pineal gland HIOMT expression (P<0.05), MLT (P<0.05) and 5-HIAA (P<0.05) levels in the 222 mg/kg group significantly increased compared to those in the CT and CT+111 mg/kg groups. In addition, the AADC (P<0.01) and AA-NAT (P<0.05) gene expression levels in the duodenum and jejunum were increased by the supplementation of RP 5-HTP. CONCLUSIONS Rumen-protected 5-hydroxytryptophan promoted melatonin synthesis in the pineal gland and intestinal tract during the natural light period.

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.

Effects of Probiotic Bacillus as an Alternative of Antibiotics on Digestive Enzymes Activity and Intestinal Integrity of Piglets

The previous study in our team found that supplementation of probiotic Bacillus amyloliquefaciens (Ba) instead of antibiotics promote growth performance of piglets. Hence, the present study was carried out to further demonstrate the effect of Ba replacement of antibiotics on digestive and absorption enzyme activity and intestinal microbiota population of piglets. A total of 90 piglets were selected and divided into three groups: G1 group was fed with basal diet supplemented with 150 mg/Kg aureomycin, G2 group was fed with 1 × 10⁸ cfu/Kg Ba and half dose of aureomycin, G3 group was used the diet with 2 × 10⁸cfu/Kg Ba replaced aureomycin. Each treatment had three replications of 10 pigs per pen. Results indicated that Ba replacement significantly increased the activities of amylase, disaccharides and Na⁺/K⁺-ATPase. And chymotrypsin activity in different section of intestine was dramatically enhanced in half replacement of aureomycin with Ba. Moreover, Ba replacement maintained the intestinal integrity with the significantly decreased activity of DAO compared with aureomycin group. Besides, supplementation with Ba increased the β-diversity of intestinal microbiota. Taken together, the current study indicated that diet supplementation with Ba instead of aureomycin increased the growth performance of piglets by improving the digestive and absorb enzyme activities, enhancing the intestinal integrity and regulating the population of intestinal micrbiota.

Effects of Dietary Zinc Oxide Nanoparticles on Growth, Diarrhea, Mineral Deposition, Intestinal Morphology, and Barrier of Weaned Piglets

This study was conducted to investigate effects of dietary zinc oxide nanoparticles (nano-ZnOs) on growth, diarrhea rate, mineral deposition (Zn, Fe, and Mn), intestinal morphology, and barrier of weaned piglets. A total of 384 weaned piglets (Duroc × Landrace × Yorkshire) in 4 groups were fed a basal diet supplemented with 0, 400, and 800 mg/kg nano-ZnOs or 3000 mg/kg ZnO for 14 days. Compared with the control group, 800 mg/kg nano-ZnOs and 3000 mg/kg ZnO significantly increased average daily gain and decreased diarrhea rate of weaned piglets. There was no significant difference among ZnO and nano-ZnO groups. ZnO and nano-ZnOs did not affect serum activities of glutamic oxalacetic transaminase, glutamic-pyruvic transaminase, and lactate dehydrogenase. However, ZnO and 800 mg/kg nano-ZnOs significantly increased zinc concentrations in plasma, liver, pancreas, and tibia, without affecting Fe and Mn concentrations. Compared with the control group, 800 mg/kg nano-ZnOs significantly reduced plasma diamine oxidase activity, decreased total aerobic bacterial population in mesenteric lymph node, enhanced mRNA expressions of occludin, ZO-1, IL-1β, IL-10, TNF-α, and ki67 in ileal mucosa, and increased villous height, width, crypt depth, and surface area. Compared to ZnO group, 800 mg/kg nano-ZnOs significantly decreased aerobic bacterial population, enhanced mRNA expressions of occludin, IL-1β, IL-10, and TNF-α, and reduced fecal zinc concentration. These results indicated that 800 mg/kg nano-ZnOs might be a potential substitute for 3000 mg/kg ZnO in diets of weaned piglets.