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-1ß, 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 genistein supplementation improves intestinal mucosal barrier function in Escherichia coli O78-challenged broilers.

Genistein has multiple biological activities in both humans and animals. However, a protective effect of genistein on Escherichia coli (E. coli)-induced intestinal mucosal barrier dysfunction remains unknown. In the present study, a total of 288 1-day-old male Arbor Acre broilers fed a corn-soybean basal diet unsupplemented or supplemented with 20 mg genistein/kg diet were subjected to E. coli serotype O78 (108 cfu per bird) infection or equal volume of sodium chloride at 19 days of age. Sera and tissue samples were collected 2 days after E. coli infection. Growth performance, index of immune-related organs, intestinal barrier permeability, protein level of inflammatory cytokines, sIgA, tight junction protein, and mRNA level of apoptotic genes in jejunum were determined. Mortality rate at 7 days post infection was recorded. The results showed that E. coli challenge led to a reduced average daily gain, a decreased thymus index, and bursal index in broilers, an increase of fluorescein isothiocyanate (FITC)-dextran in serum, and a decreased sIgA in jejunum. These effects were abrogated by genistein administration. Western blot results showed that E. coli infection led to increased protein level of claudin-1 and zonula occludens (ZO)-1, which was largely abolished by genistein. Moreover, E. coli infection resulted increased protein level of TNF-α and IL-6, enhanced mRNA level of Bax and caspase-3, as well as decreased mRNA level of Bcl-2 were abrogated by genistein in jujunum of broilers. In conclusion, the results indicate that genistein supplementation improves intestinal mucosal barrier function which is associated with a regulatory effect on tight junction proteins, sIgA, apoptosis, and secretion of inflammatory cytokines in jejunum of E. coli-challenged broilers.

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-1ß, 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 l-Tryptophan Supplementation Enhances the Intestinal Mucosal Barrier Function in Weaned Piglets: Implication of Tryptophan-Metabolizing Microbiota.

l-Tryptophan (Trp) is known to play an important role in the health of the large intestine. However, a role of dietary Trp in the small-intestinal mucosal barrier and microbiota remains poorly understood. The present study was conducted with weaned piglets to address this issue. Postweaning piglets were fed for 4 weeks a corn- and soybean meal-based diet supplemented with 0 (Control), 0.1, 0.2, or 0.4% Trp. The small-intestinal microbiota and serum amino acids were analyzed by bacterial 16S rRNA gene-based high-throughput sequencing methods and high-performance liquid chromatography, respectively. The mRNA levels for genes involved in host defense and the abundances of tight-junction proteins in jejunum and duodenum were measured by real time-PCR and Western blot techniques, respectively. The concentrations of Trp in the serum of Trp-supplemented piglets increased in a dose-dependent manner. Compared with the control group, dietary supplementation with 0.2⁻0.4% Trp reduced the abundances of Clostridium sensu stricto and Streptococcus in the jejunum, increased the abundances of Lactobacillus and Clostridium XI (two species of bacteria that can metabolize Trp) in the jejunum, and augmented the concentrations of secretory immunoglobulin A (sIgA) as well as mRNA levels for porcine ß-defensins 2 and 3 in jejunal tissues. Moreover, dietary Trp supplementation activated the mammalian target of rapamycin signaling and increased the abundances of tight-junction proteins (zonula occludens (ZO)-1, ZO-3, and claudin-1) in jejunum and duodenum. We suggested that Trp-metabolizing bacteria in the small intestine of weaned pigs primarily mediated the beneficial effects of dietary Trp on its mucosal integrity, health, and function.