Tryptophan promoted β-defensin-2 expressionviathe mTOR pathway and its metabolites: kynurenine banding to aryl hydrocarbon receptor in rat intestine

Neurodevelopmental implications of COVID-19-induced gut microbiome dysbiosis in pregnant women

The global public health emergency of COVID-19 in January 2020 prompted a surge in research focusing on the pathogenesis and clinical manifestations of the virus. While numerous reports have been published on the acute effects of COVID-19 infection, the review explores the multifaceted long-term implications of COVID-19, with a particular focus on severe maternal COVID-19 infection, gut microbiome dysbiosis, and neurodevelopmental disorders in offspring. Severe COVID-19 infection has been associated with heightened immune system activation and gastrointestinal symptoms. Severe COVID-19 may also result in gut microbiome dysbiosis and a compromised intestinal mucosal barrier, often referred to as 'leaky gut'. Increased gut permeability facilitates the passage of inflammatory cytokines, originating from the inflamed intestinal mucosa and gut, into the bloodstream, thereby influencing fetal development during pregnancy and potentially elevating the risk of neurodevelopmental disorders such as autism and schizophrenia. The current review discusses the role of cytokine signaling molecules, microglia, and synaptic pruning, highlighting their potential involvement in the pathogenesis of neurodevelopmental disorders following maternal COVID-19 infection. Additionally, this review addresses the potential of probiotic interventions to mitigate gut dysbiosis and inflammatory responses associated with COVID-19, offering avenues for future research in optimizing maternal and fetal health outcomes.

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.

Tryptophan alleviates lipopolysaccharide-induced muscle fiber type transformation from type I to II and modulates Sirt1/AMPK/PGC-1α signaling pathway in pigs

Tryptophan is a functional amino acid. This study aimed to investigate whether dietary tryptophan supplementation can alleviate Escherichia coli lipopolysaccharide (LPS)-induced skeletal muscle fiber transition from type I to type II in pigs, and the molecular mechanism was also examined. Eighteen weaned piglets were allotted to three treatments groups, namely, the nonchallenged control, LPS-challenged control and LPS + 0.2% tryptophan groups. On day 35, the pigs in the LPS and LPS + 0.2% tryptophan groups were challenged by injection with 100 μg/kg body weight (BW) LPS, whereas the control group was given sterile saline. Tryptophan can attenuate LPS-induced decrease in protein content of slow MyHC, the activities of succinic dehydrogenase, malate dehydrogenase (MDH) and antioxidant enzyme, the mRNA expression of oxidative muscle fiber-related genes, type I fiber proportion, and increase in lactate dehydrogenase (LDH) activity, the mRNA expression level of MyHC IIb and type II fiber proportion. Moreover, tryptophan supplementation attenuated LPS-induced decrease in the expression levels of phosphorylated AMP-activated protein kinase (AMPK), silent information regulator 1 (Sirt1) and peroxisome proliferator activated receptor gamma coactivator 1-alpha (PGC-1α). Collectively, tryptophan can alleviate LPS-induced muscle fiber type transformation from type I to type II. This effect is associated with activating the Sirt1/AMPK/PGC-1α signaling pathway.

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.

Host Defense Peptides in Nutrition and Diseases: A Contributor of Immunology Modulation

Host defense peptides (HDPs) are primary components of the innate immune system with diverse biological functions, such as antibacterial ability and immunomodulatory function. HDPs are produced and released by immune and epithelial cells against microbial invasion, which are widely distributed in humans, animals, plants, and microbes. Notably, there are great differences in endogenous HDP distribution and expression in humans and animals. Moreover, HDP expression could be regulated by exogenous substances, such as nutrients, and different physiological statuses in health and disease. In this review, we systematically assessed the regulation of expression and mechanism of endogenous HDPs from nutrition and disease perspectives, providing a basis to identify the specificity and regularity of HDP expression. Furthermore, the regulation mechanism of HDP expression was summarized systematically, and the differences in the regulation between nutrients and diseases were explored. From this review, we provide novel ideas targeted the immune regulation of HDPs for protecting host health in nutrition and practical and effective new ideas using the immune regulation theory for further research on protecting host health from pathogenic infection and excessive immunity diseases under the global challenge of the antibiotic-abuse-induced series of problems, including food security and microbial resistance.

Dietary Tryptophan Supplementation Improves Antioxidant Status and Alleviates Inflammation, Endoplasmic Reticulum Stress, Apoptosis, and Pyroptosis in the Intestine of Piglets after Lipopolysaccharide Challenge

Tryptophan can alleviate stress and improve intestinal health, but the precise mechanism has not been fully elucidated. This study aimed to examine the effects of tryptophan supplementation on antioxidant status, inflammation, endoplasmic reticulum (ER) stress, apoptosis, and pyroptosis signaling pathway in the intestine of piglets after Escherichia coli lipopolysaccharide (LPS) challenge. Thirty-two weaning piglets were allotted to four treatments including: non-challenged control, LPS-challenged control, LPS + 0.2% tryptophan and LPS + 0.4% tryptophan. On day 35 of feeding, piglets were injected intraperitoneally with 100 μg/kg of body weight LPS or saline. Among the LPS-challenged pigs, tryptophan supplementation improved intestinal morphology as indicated by greater villus height, villus area and smaller crypt depth, and antioxidant status, and decreased the mRNA expression and concentration of proinflammatory cytokines. Moreover, tryptophan downregulated the expression of ER stress (ER oxidoreductase-1α, ER oxidoreductase-1β, glucose-regulated protein-78, activating transcription factor 6, C/EBP homologous protein), apoptosis (B-cell lymphoma-2, BCL2-associated X protein, caspase 3), and pyroptosis signaling pathway (nucleotide-binding oligomerization domain-like receptor protein 3, caspase 1, gasdermin-D, apoptosis-associated speck-like protein containing a CARD). Collectively, tryptophan supplementation can contribute to gut health by improving antioxidant status and alleviating inflammation, ER stress, apoptosis, and pyroptosis in the intestine of piglets after lipopolysaccharide challenge.

Tryptophan Promotes Intestinal Immune Defense through Calcium-Sensing Receptor (CaSR)-Dependent Metabolic Pathways

The gastrointestinal tract forms a robust line of defense against invading pathogens through the production of endogenous antimicrobial peptides (AMPs), which are crucial molecules of the innate defense system. Tryptophan could modulate intestinal immunity through promoting the expression of AMPs. However, the precise mechanism needs to be further clarified. In this study, we show that treatment with tryptophan for 24 h triggers (p < 0.05) the expression of porcine β-defensin (pBD) 1 (62.67 ± 3.10 pg/mL) and pBD2 (74.41 ± 1.33 pg/mL) in the porcine intestinal epithelial cells (IPEC-J2) though calcium-sensing receptor (CaSR)-tryptophan metabolic pathways. Meanwhile, tryptophan alleviates (p < 0.05) intestinal inflammation induced by lipopolysaccharide (LPS) through induction of the defensins and activation of the CaSR-AMP-activated protein kinase (AMPK) pathways in vitro and in vivo. Moreover, the activation of CaSR induces the expression of defensins and decreases the levels of IL-1β (75.26 ± 2.74 pg/mL) and TNF-α (449.8 ± 23.31 pg/mL) induced by LPS (p < 0.05). Importantly, tryptophan maintains kynurenine homeostasis through the activation of CaSR during the inflammatory response. To that end, the work identifies a regulatory circuit between CaSR signaling and tryptophan metabolic pathways involved in the tryptophan-trigged AMP expression, which contributes to improving intestinal immune defense.

Tryptophan Ameliorates Barrier Integrity and Alleviates the Inflammatory Response to Enterotoxigenic Escherichia coli K88 Through the CaSR/Rac1/PLC-γ1 Signaling Pathway in Porcine Intestinal Epithelial Cells

Background

Impaired intestinal barrier integrity plays a crucial role in the development of many diseases such as obesity, inflammatory bowel disease, and type 2 diabetes. Thus, protecting the intestinal barrier from pathological disruption is of great significance. Tryptophan can increase gut barrier integrity, enhance intestinal absorption, and decrease intestinal inflammation. However, the mechanism of tryptophan in decreasing intestinal barrier damage and inflammatory response remains largely unknown. The objective of this study was to test the hypothesis that tryptophan can enhance intestinal epithelial barrier integrity and decrease inflammatory response mediated by the calcium-sensing receptor (CaSR)/Ras-related C3 botulinum toxin substrate 1 (Rac1)/phospholipase Cγ1 (PLC-γ1) signaling pathway.

Methods

IPEC-J2 cells were treated with or without enterotoxigenic Escherichia coli (ETEC) K88 in the absence or presence of tryptophan, CaSR inhibitor (NPS-2143), wild-type CaSR overexpression (pcDNA3.1-CaSR-WT), Rac1-siRNA, and PLC-γ1-siRNA.

Results

The results showed that ETEC K88 decreased the protein concentration of occludin, zonula occludens-1 (ZO-1), claudin-1, CaSR, total Rac1, Rho family member 1 of porcine GTP-binding protein (GTP-rac1), phosphorylated phospholipase Cγ1 (p-PLC-γ1), and inositol triphosphate (IP3); suppressed the transepithelial electrical resistance (TEER); and enhanced the permeability of FITC-dextran compared with the control group. Compared with the control group, 0.7 mM tryptophan increased the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; elevated the TEER; and decreased the permeability of FITC-dextran and contents of interleukin-8 (IL-8) and TNF-α. However, 0.7 mM tryptophan+ETEC K88 reversed the effects induced by 0.7 mM tryptophan alone. Rac1-siRNA+tryptophan+ETEC K88 or PLC-γ1-siRNA+tryptophan+ETEC K88 reduced the TEER, increased the permeability of FITC-dextran, and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. NPS2143+tryptophan+ETEC K88 decreased the TEER and the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; increased the permeability of FITC-dextran; and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. pcDNA3.1-CaSR-WT+Rac1-siRNA+ETEC K88 and pcDNA3.1-CaSR-WT+PLC-γ1-siRNA+ETEC K88 decreased the TEER and enhanced the permeability in porcine intestine epithelial cells compared with pcDNA3.1-CaSR-WT+ETEC K88.

Conclusion

Tryptophan can improve intestinal epithelial barrier integrity and decrease inflammatory response through the CaSR/Rac1/PLC-γ1 signaling pathway.

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.

L-Threonine upregulates the expression of β-defensins by activating the NF-κB signaling pathway and suppressing SIRT1 expression in porcine intestinal epithelial cells

The use of antimicrobial peptide (AMP), found in all forms of life and playing a pivotal role in the innate immune system, has been developed as a new strategy for maintaining intestinal health and reducing antibiotic usage due to its ability to resist pathogens and commensal microbes. The current study investigated the effects of l-threonine on β-defensin expression, the intestinal mucosal barrier and inflammatory cytokine expression in porcine intestinal epithelial cell lines (IPEC-J2). The results revealed that in IPEC-J2 cells, l-threonine significantly increased the expression of β-defensin (including pBD-1, pBD-2, and pBD-3) in a dose- and time-dependent manner (P < 0.05). By using different concentrations and treatment times of l-threonine, the results showed that the expression of β-defensin was upregulated to the greatest extent in IPEC-J2 cells cultured with 1 mM l-threonine for 24 h. Although the mRNA expression levels of β-defensins were markedly increased (P < 0.05), there was relatively little inducible pBD-1, pBD-2 and pBD-3 mRNA expression at the sub-confluent and confluent densities in comparison with post-confluent densities. Furthermore, we found that l-threonine enhanced the β-defensin expression by suppressing the expression of SIRT1, which increased acetylated p65 expression, and activating the NF-κB signaling pathway, which induced the translocation of p65 from the cytoplasm to the nucleus. In addition, l-threonine significantly prevented LPS-induced intestinal mucosal barrier damage by attenuating the decreasing tendency of the mRNA expression of Mucin1 and Mucin2 (P < 0.05). Simultaneously, l-threonine enhanced the expression of β-defensins upon LPS challenge in IPEC-J2 cells (P < 0.05). l-Threonine obviously decreased the mRNA expression of inflammatory cytokines compared to that in untreated cells (P < 0.05). In conclusion, l-threonine can upregulate β-defensin expression and reduce inflammatory cytokine expression in IPEC-J2 cells; meanwhile, l-threonine alleviates LPS-induced intestinal mucosal barrier damage in porcine intestinal epithelial cells. The l-threonine-mediated modulation of endogenous defensin expression may be a promising approach to reduce antibiotic use, enhance disease resistance and intestinal health in animals.